Cuanto más inteligentes, más proclives a sesgos cognitivos

El caparazón: Cuanto más inteligentes, más proclives a sesgos cognitivos

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Cuanto más inteligentes, más proclives a sesgos cognitivos Posted: 13 Jun 2012 11:40 PM PDT El titular resulta contraintuitivo. Como casi todo lo que Daniel Kahneman, premio nobel y uno de los psicólogos más respetados de nuestro tiempo, nos cuenta enThinking Fast and Slow, uno de los libros que tengo casi terminado por el escritorio. Su propuesta, trabajada con Amos Tversky y otros psicólogos de la cognición humana, consiste en demostrar cómo de irracionales somos en el fondo, cómo de susceptibles a los más diversos errores cognitivos nos mostramos y cómo la mayor parte del tiempo nos dejamos llevar por el tipo de pensamiento rápido, superficial, aparentemente intuitivo que nos domina la mayor parte del tiempo. Cuando nos enfrentamos a una nueva situación no evaluamos cuidadosamente la información ni realizamos complicados cálculos estadísticos sino que tomamos uno de los numerosos atajos cognitivos que suelen llevarnos a tomar decisiones erróneas. Pues bien… un nuevo estudio en el Journal of Personality and Social Psychology  que descubro en The New yorker sugiere que además, contra lo que pudiera parecer, la gente más inteligente es más vulnerable a este tipo de errores en el pensamiento. La investigación consistía en pasar a 482 participantes un cuestionario con distintos problemas de sesgo clásicos, como los que podéis encontrar en el libro citado de Kahneman. Aquí un ejemplo de los que se citan en la investigación: Tenemos en un lago  una zona de hojas de nenúfar. Cada día se duplica en tamaño. Si se tarda 48 días en que cubra todo el lago, ¿cuánto tiempo tardará en cubrir la mitad del lago? (Pues sí, parece que lo más fácil es dividir la respuesta por dos, quedando en 24 días. Pues no es correcto, el pensamiento exponencial no es fácil ni intuitivo y … la solución sería 47 días. ) Los resultados eran sorprendentes y mostraban cómo la inteligencia, lo que los investigadores llamaban la sofisticación cognitiva y contra todas las críticas a Kahneman por  investigar lo que muchos pensaban la psicología de la estupidez, correlacionaba con más irracionalidad. En concreto parece que la gente más inteligente era más vulnerable a los errores mentales comunes.  La autoconciencia, además, no ayudaba… y los que eran más conscientes de sus propios fallos cognitivos no tendían a cometerlos en menor medida (precisamente, como veremos, porque estos son inconscientes) Una de las posibles hipótesis está en considerar la fuerza del “meta-sesgo” de la tendencia natural a asumir que cualquier otra persona es más susceptible de cometer errores cognitivos que nosotros mismos. El denominado sesgo del punto ciego consiste en aquello de “ver la paja en el ojo ajeno y no la viga en el propio”,  estableciendo una diferencia crucial entre cómo evaluamos a los demás y cómo nos evaluamos a nosotros mismos. En este sentido, cuando consideramos las elecciones irracionales de un extraño nos vemos obligados a confiar en información comportamental, vemos sus fallos desde fuera y somos capaces de detectarlos, pero cuando nos valoramos a nosotros mismos elaboramos las cosas de forma introspectiva. Siendo los motivos de los sesgos mayoritariamente inconscientes, son elusivos precisamente a eso, a la introspección, al autoanálisis y la inteligencia. Si unimos lo anterior a lo que explicábamos en un post reciente sobre la ignorancia como gran creadora de historias, veremos claramente cómo la introspección puede incluso ser perjudicial, cegando y ayudando a construir historias más elocuentes pero erróneas  a la gente con mayor puntuación en los tests. ¿Se aplica al autoconocimiento más que a cualquier otra forma de conocimiento la máxima socrática de “solo sé que no sé nada” o la sensación subjetiva de que cuanto más se sabe mayor es la sensación de que queda mucho por conocer?  Puede que cuanto más intentemos conocernos a nosotros mismos más nos alejemos de hacerlo… La anterior sería una posible explicación pero habiendo leído a Kahneman hay detalles que no me cuadran. Según el autor, es infrecuente pero posible es la puesta en marcha de un sistema de pensamiento más reflexivo, consciente, racional que el primero, capaz de detectar los errores y de no cometerlos. Es probable que el tema no se aplique igual a la autoevaluación que a la ajena pero se me ocurre una última explicación para los resultados de la investigación y es que  podría ser que todo se debiese a una cuestión de expectativas sobre la autoeficacia: conocida es la imprecisión de los sistemas de medición de la inteligencia (en este caso S.A.T. y la escala Need for Cognition, que mide la tendencia a implicarse y disfrutar del pensamiento), más desde que se mira a la misma desde un punto de vista simplista en tiempos de multi-inteligencias (de eso hablaremos en un ratito en La Red Innova). A pesar de ello el hecho de pasar un test clásico con buena puntuación genera unas expectativas acerca de uno mismo que pueden hacer a los que puntúan alto excesivamente confiados, procesando problemas con el sistema automático porque se valora que no vale la pena poner de marcha el otro, que se es lo suficientemente inteligente como para dejar que lo automático decia. La gente por debajo o en la media, sin embargo, no se confiaría y trabajaría duro, pondría en marcha los sistemas más “racionales” para resolver las cosas. En fin… que surge de nuevo la educación emocional como clave. Todo dependerá del autoconcepto porque volviendo a un post anterior, no somos todo lo genios que nos dicen que somos y lo único válido es el valor del esfuerzo. Además, lo decíamos hace tiempo sobre Gardner y las inteligencias múltiples, la globalización de los conceptos que vivimos nos traerá muchas más,diversas y justas formas de inteligencia… ¿Qué pasará con el talento en una sociedad-red en la que más personas y más diversas tienen más posibilidades, más independientes de los condicionantes de poder tradicionales, de demostrarlo?

In Good Health? Thank Your 100 Trillion Bacteria

By GINA KOLATA

Published: June 13, 2012

For years, bacteria have had a bad name. They are the cause of infections, of diseases. They are something to be scrubbed away, things to be avoided.

But now researchers have taken a detailed look at another set of bacteria that may play even bigger roles in health and disease: the 100 trillion good bacteria that live in or on the human body.

No one really knew much about them. They are essential for human life, needed to digest food, to synthesize certain vitamins, to form a barricade against disease-causing bacteria. But what do they look like in healthy people, and how much do they vary from person to person?

In a new five-year federal endeavor, the Human Microbiome Project, which has been compared to the Human Genome Project, 200 scientists at 80 institutionssequenced the genetic material of bacteria taken from nearly 250 healthy people.

They discovered more strains than they had ever imagined — as many as a thousand bacterial strains on each person. And each person’s collection of microbes, the microbiome, was different from the next person’s. To the scientists’ surprise, they also found genetic signatures of disease-causing bacteria lurking in everyone’s microbiome. But instead of making people ill, or even infectious, these disease-causing microbes simply live peacefully among their neighbors.

The results, published on Wednesday in Nature and three PLoS journals, are expected to change the research landscape.

The work is “fantastic,” said Bonnie Bassler, a Princeton University microbiologist who was not involved with the project. “These papers represent significant steps in our understanding of bacteria in human health.”

Until recently, Dr. Bassler added, the bacteria in the microbiome were thought to be just “passive riders.” They were barely studied, microbiologists explained, because it was hard to know much about them. They are so adapted to living on body surfaces and in bodycavities, surrounded by other bacteria, that many could not be cultured and grown in the lab. Even if they did survive in the lab, they often behaved differently in this alien environment. It was only with the advent of relatively cheap and fast gene sequencing methods that investigators were able to ask what bacteria were present.

Examinations of DNA sequences served as the equivalent of an old-time microscope, said Curtis Huttenhower of the Harvard School of Public Health, an investigator for the microbiome project. They allowed investigators to see — through their unique DNA sequences — footprints of otherwise elusive bacteria.

The work also helps establish criteria for a healthy microbiome, which can help in studies of how antibiotics perturb a person’s microbiome and how long it takes the microbiome to recover.

In recent years, as investigators began to probe the microbiome in small studies, they began to appreciate its importance. Not only do the bacteria help keep people healthy, but they also are thought to help explain why individuals react differently to various drugs and why some are susceptible to certain infectious diseases while others are impervious. When they go awry they are thought to contribute to chronic diseases and conditions likeirritable bowel syndrome, asthma, even, possibly, obesity.

Humans, said Dr. David Relman, a Stanford microbiologist, are like coral, “an assemblage of life-forms living together.”

Dr. Barnett Kramer, director of the division of cancer prevention at the National Cancer Institute, who was not involved with the research project, had another image. Humans, he said, in some sense are made mostly of microbes. From the standpoint of our microbiome, he added, “we may just serve as packaging.”

The microbiome starts to grow at birth, said Lita Proctor, program director for the Human Microbiome Project. As babies pass through the birth canal, they pick up bacteria from the mother’s vaginal microbiome.

“Babies are microbe magnets,” Dr. Proctor said. Over the next two to three years, the babies’ microbiomes mature and grow while their immune systems develop in concert, learning not to attack the bacteria, recognizing them as friendly.

Babies born by Caesarean section, Dr. Proctor added, start out with different microbiomes, but it is not yet known whether their microbiomes remain different after they mature. In adults, the body carries two to five pounds of bacteria, even though these cells are minuscule — one-tenth to one-hundredth the size of a human cell. The gut, in particular, is stuffed with them.

“The gut is not jam-packed with food; it is jam-packed with microbes,” Dr. Proctor said. “Half of your stool is not leftover food. It is microbial biomass.” But bacteria multiply so quickly that they replenish their numbers as fast as they are excreted.

The bacteria also help the immune system, Dr. Huttenhower said. The best example is in the vagina, where they secrete chemicals that can kill other bacteria and make the environment slightly acidic, which is unappealing to other microbes.

Including the microbiome as part of an individual is, some researchers said, a new way to look at human beings.

It was a daunting task, though, to investigate the normal human microbiome. Previous studies of human microbiomes had been small and had looked mostly at fecal bacteria or bacteria in saliva in healthy people, or had examined things like fecal bacteria in individuals with certain diseases, like inflammatory bowel disease, in which bacteria are thought to play a role.

But, said Barbara B. Methé, an investigator for the microbiome study and a microbiologist at the J. Craig Venter Institute, it was hard to know what to make of those studies.

“We were stepping back and saying, ‘We don’t really have a population study. What does a normal microbiome look like?’ ” she said.

The first problem was finding completely healthy people for the study. The investigators recruited 600 subjects, ages 18 to 40, poking and prodding them. They brought in dentists to probe their gums, looking for gum disease, and pick at their teeth, looking for cavities. They brought in gynecologists to examine the women to see if they had yeast infections. They examined skin and tonsils and nasal cavities. They made sure the subjects were not too fat and not too thin. Even though those who volunteered thought they filled the bill, half were rejected because they were not completely healthy. And 80 percent of those who were eventually accepted first had to have gum disease or cavities treated by a dentist.

When they had their subjects — 242 men and women deemed free of disease in the nose, skin, mouth, gastrointestinal tract and, for the women, vagina — the investigators collected stool samples and saliva, and scraped the subjects’ gums and teeth and nostrils and their palates and tonsils and throats. They took samples from the crook of the elbow and the folds of the ear. In all, women were sampled in 18 places, including three sites in the vagina, and men in 15. The investigators resampled subjects three times during the course of the study to see if the bacterial composition of their bodies was stable, generating 11,174 samples.

To catalog the body’s bacteria, researchers searched for DNA with a specific gene, 16S rRNA, that is a marker for bacteria and whose slight sequence variations can reveal different bacterial species. They sequenced the bacterial DNA to find the unique genes in the microbiome. They ended up with a deluge of data, much too much to study with any one computer, Dr. Huttenhower said, creating “a huge computational challenge.”

The next step, he said, is to better understand how the microbiome affects health and disease and to try to improve health by deliberately altering the microbiome.

But, Dr. Relman said, “we are scratching at the surface now.”

It is, he said, “humbling.”

A version of this article appeared in print on June 14, 2012, on page A24 of the New York edition with the headline: In Good Health? Thank Your 100 Trillion Bacteria
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Reflexiones de los médicos en formación sobre la seguridad del paciente

Reflexiones de los médicos en formación sobre la seguridad del paciente Junior doctors' reflections on patient safety Maria Ahmed, Sonal Arora, Simon Carley, Nick Sevdalis, Graham Neale Postgrad Med J 2012;88:125e129. doi:10.1136/postgradmedj-2011-130301 ABSTRACT Aim To determine whether foundation year 1 (FY1) doctors reflect upon patient safety incidents (PSIs) within their portfolios and the potential value of such reflections for quality of care. Methods A cross-sectional retrospective review of every 'reflective practice' portfolio entry made by all FY1 doctors within an Acute Teaching Hospital Trust was conducted in February 2010. Entries were reviewed by two independent blinded researchers to determine whether they related to a PSI that is, any unintended or unexpected incident that could have or did lead to patient harm. For all entries rated positive by both reviewers, a content analysis approach was used to code PSI into incident type, contributing factors and patient outcome according to validated frameworks developed by the National Patient Safety Agency. Results 139 reflective practice entries were completed by 30 trainees (15 men, 15 women, mean age 24 years). Of the 139 entries, 49% reflected on a PSI. Of these, 22% were due to errors in clinical assessment; 22% were due to delayed access to care; 18% were due to infrastructure/staffing deficiencies; and 16% were due to medication errors. The most common contributing factors were team/social factors (23%), patient factors (22%), communication and task factors (both 17%). The majority of PSIs led to no harm. Six entries described PSIs resulting in patient death, the majority of which were attributable to diagnostic errors. Conclusions FY1 doctors commonly reflect on PSIs within their professional portfolios. Such critical reflection can encourage learning but may also promote patient safety and the quality of healthcare across all medical specialties http://pmj.bmj.com/content/88/1037/125.full.pdf+html

Atentamente Anestesiología y Medicina del Dolor www.anestesia-dolor.org

Estrategia de eSalud para Latinoamérica

Somos Medicina

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Estrategia de eSalud para Latinoamérica Posted: 12 Jun 2012 10:00 PM PDT Pocas veces tenemos la ocasión de conocer de primera mano las estrategias de eSalud que proyectan para el futuro organismos internacionales como la OMS. Hace poco esta misma organización publicaba un boletín monográfico sobre los avances en eSalud por todo el mundo, esta vez podemos acercarnos un poco más al modelo de eSalud de la OMS. Desde hace unos días está disponible esta presentación de Eliane Pereira dos Santos, asesora regional de la PAHO a través de la Oficina del Director del Área de Gestión del Conocimiento y las Comunicaciones (KMC). En la presentación se hace un recorrido por los hitos previos que han condicionado la postura actual de la OMS hacia la eSalud y se explican los puntos claves de la estrategia y plan de acción sobre eSalud (2012-2017) divididos en cuatro áreas estratégicas: Respaldar y promover la formulación, la ejecución y la evaluación de las políticas públicas eficaces, integradas y sostenibles sobre el uso y la implantación de las tecnologías de la información y de las comunicaciones en el ámbito sanitario Mejorar la salud públca por medio del uso de herramientas y metodologías basadas en tecnologías innovadoras de la información de de las comunicaciones Fomentar y facilitar la colaboración horizontal entre los países para el desarrollo de una Agenda Digital en materia de salud para la Región Gestión del conocimiento y formación en alfabetización digital y tecnologías de la información y la comunicación como elementos clave para la calidad asistencial, la promoción y la prevención de enfermedades, garantizando la capacitación y el mejor acceso a la información de manera equitativa Si queréis profundizar en la Estrategia y plan de acción sobre eSalud para Latinoamérica de la PAHO/OMS os recomiendo la lectura completa del punto 4.10 en el orden del día de la 51ª Reunión del Consejo Directivo que tuvo lugar en Washington del 26 al 30 de Septiembre de 2011 y donde se detallan todos los objetivos que espera lograr la OMS durante los próximos años en el campo de la eSalud.

La expansión de la lectura

Publicado por Joaquín Rodríguez el 12 junio, 2012

Comentarios (1)

A menudo nos perdemos en una discusión banal y fútil basada en una equivocación: leer no es sólo, hoy en día, conformarse con lo que la textualidad tradicional nos proporciona, con una arquitectura del conocimiento construída exclusivamente con libros. Esa afirmación no entraña negación alguna, menos aún devaluación: leer textos sucesivos, linealmente, siguiendo un argumento complejo y empeñándonos en reflexionar sobre el contenido que nos aporta, es, seguramente, una de las experiencias de aprendizaje más profundas que un ser humano pueda experimentar. Pero, siendo eso así, ¿quién puede negar que hoy en día aprender a leer debe entrañar, simultáneamente, la capacidad de reconstruir y regenerar el sentido, críticamente, a partir de muy distintas fuentes y formatos (webs, vídeos, podcast, contenidos multimedia e interactivos, bases de datos, gráficos, tablas, etc.).?

Leer, en el siglo XXI, es una tarea poliédrica que atañe a todas las áreas de conocimiento y a todas las etapas de la educación: atañe por igual a la lectura profunda tradicional y a la lectura de la información contenida en distintos soportes y formatos a partir de la cual debe exigírsele al lector la capacidad de generar una síntesis crítica que pueda utilizar para su propósito y sus objetivos. Leer es una actividad multidimensional, multimedia y multipropósito, y plantear currícula que afronten esa realidad de manera urgente, es una tarea imperativa.

En Estados Unidos Henry Jenkins había ya trazado una suerte de áreas prioritarias del currículum en el siglo XXI en el documento Confronting the challenges of participatory culture. Media education for the 21st Century, y la International Society for Technology Education fijó losestándares y objetivos que debían incluirse en la formación de alumnos, profesores y administradores.

En Europa, poco a poco, la necesidad se percibe como una misión ineludible y urgente -aun cuando todavía peroran sin descanso contra toda forma de lectura expandida quienes vivieron tanto tiempo de las letras tradicionales-:  el Joint Research Centre de la Unión Europea ha puesto recientemente en marcha el programa Digital competence: identification and European-wide validation of its key components for all levels of learners (DIGCOMP), se está trabajando en el desarrollo del primer mapa conceptual comprehensivo de esas competencias digitalesfundamento de la nueva alfabetización complementaria, y se ha creado la European e‐Skills Association (EeSA), para la promoción de una nueva forma de alfabetización y lectura extendida.

Leer es formar ciudadanos alfabetizados en el uso y valoración crítica de las diversas fuentes de contenidos que nos aportan información en el siglo XXI; leer es darles las herramientas, filtros y capacidades para hilar los muy diversos mensajes que los diversos medios nos presentan; leer es reconstruir el sentido fragmentario y complejo de una realidad dispersa. De ahí la necesidad de expandir la definición tradicional de leer, expandiendo su ámbito y su complejidad. No es asumible ni serio, por eso, realizar declaraciones como las de Jordi Llovet, unidimensionales y harto conservadoras en su planteamiento: “el autor considera importante”, dice refiriéndose a él mismo en tercera persona, “retroceder hasta formas pretecnológicas de la enseñanza, de la información y de la discusión intelectual, en las que haya quedado incólume la dignidad de la palabra y la posibilidad de generar razonamiento, conocimiento, conversacion y sabiduría comunal”. Tentando estoy de asegurar que ya vivimos hace demasiado tiempo en entornos educativos pretecnológicos y cuasimediavales y que lo que nos hace falta, en todo caso, es una definición inclusiva de alfabetización digital.

Dentro de unos pocos días, el 19-20 de junio, se celebrará el primer Seminario internacional en Alfabetización informacional y  multimedia en Fez, Marruecos, convocado por la UNESCO, porque se trata de una necesidad global, no de un empeño local.

Actualidades medicas

Special Articles
Evidence-based guideline update: Pharmacologic treatment for episodic migraine prevention in adults: Report of the Quality Standards Subcommittee of the American Academy of Neurology and the American Headache Society

ABSTRACT
Objective: To provide updated evidence-based recommendations for the preventive treatment of migraine headache. The clinical question addressed was: What harmacologic therapies are proven effective for migraine prevention?
Methods: The authors analyzed published studies from June 1999 to May 2009 using a structured review process to classify the evidence relative to the efficacy of various medications available in the United States for migraine prevention.
Results and Recommendations: The author panel reviewed 284 abstracts, which ultimately yielded 29 Class I or Class II articles that are reviewed herein. Divalproex sodium, sodium valproate, topiramate, metoprolol, propranolol, and timolol are effective for migraine prevention and should be offered to patients with migraine to reduce migraine attack frequency and severity (Level A). Frovatriptan is effective for prevention of menstrual migraine (Level A). Lamotrigine is ineffective for migraine prevention (Level A). 
Neurology® 2012;78:1337–1345

Emergency Medicine Clinics of North America

Copyright © 2011 W. B. Saunders Company  -  About This Clinic     Add Clinics Issue Alert 

Volume 29, Issue 2 (May, 2011)

Issue Contents: (Pages iii-458)

iii-v	Contributors No Author PDF
xi-xi	Forthcoming Issues No Author PDF
xii-xii	CME Accreditation Page and Author Disclosure No Author PDF
xiii-xiv	Foreword Mattu A PDF
xv-xvii	Preface Mills AM PDF
159-173	Approach to Acute Abdominal Pain McNamara R PDF
175-193	Imaging and Laboratory Testing in Acute Abdominal Pain Panebianco NL PDF
195-210	Systemic Causes of Abdominal Pain Fields JM PDF
211-237	Vomiting, Diarrhea, Constipation, and Gastroenteritis Getto L PDF
239-252	Gastrointestinal Bleeding Kumar R PDF
253-272	Vascular Abdominal Emergencies Lewiss RE PDF
273-291	Gastric and Esophageal Emergencies Mangili A PDF
293-317	Emergencies of the Liver, Gallbladder, and Pancreas Privette TW PDF
319-345	Bowel Obstruction and Hernia Hayden GE PDF
347-368	Appendicitis, Diverticulitis, and Colitis Horn AE PDF
369-400	Foreign Bodies in the Gastrointestinal Tract and Anorectal Emergencies Anderson KL PDF
401-428	Abdominal Pain in Children Marin JR PDF
429-448	Acute Abdominal Pain in the Older Adult Ragsdale L PDF
449-458	Abdominal Pain in Special Populations Chen EH PDF

 

Atte.

Dr.Máximo Cuadros Chávez

Choosing a Sugar Substitute

FOOD | 

By KENNETH CHANG

 | June 11, 2012, 2:10 PM 461 Comments

Aimee McHale Chapel Hill

I live in the South, where sweet iced tea is obligatory. Rather than indulging in sweet tea, which is incredibly sweet and highly caloric, I order unsweet tea and add Sweet 'N Low ... because, as any good Southerner knows, it's the only artificial sweetener that dissolves in ice cold water.

• RECOMMEND
• June 12, 2012 at 7:35 a.m.

Tony Cenicola/The New York TimesWatch the sweetener packets to see what readers are saying about sweeteners. Post your own comment below and it may appear in the display.

On restaurant tables everywhere, the colors of the sweetener packets instantly identify the contents.White. Pink. Blue. Yellow.

Sugar. Saccharin. Aspartame. Sucralose.

Reaching for one to pour into a cup of coffee or tea can sometimes feel like sweetener roulette, with the swirl of confusing, conflicting assertions about which are safe and which are not.

Alissa Kaplan Michaels, for one, never picks pink. She still associates saccharin with cancer. The Food and Drug Administration sought to ban it in the 1970s, because rats that gorged on the chemical developed bladder cancer.

But Congress imposed a moratorium to delay the ban, and the pink packets of Sweet’N Low remained on restaurant tables. The F.D.A. withdrew its ban proposal in 1991, and the warnings were taken off saccharin in 2000 after research showed that it acts differently in rats and humans, and no conclusive increase in cancers was observed in people. Ms. Michaels, a public relations consultant in New York, knows this.

But, she said, “It’s the cancer in the rats. I can’t get that out of my head.”

Although many people have nagging worries about artificial sweeteners, they still use mountains of them — globally, artificial sweeteners are a $1.5-billion-a-year market — to avoid sugar and calories.

The scientific world is also a dichotomy of conclusions. For any of the sweeteners, one can as easily find a study that offers reassuring analysis of safety as one that enumerates potential alarming effects. And it is possible that there could be long-term effects in humans that will become evident only after people have been consuming these sweeteners for decades.

Thus hearsay, mythology and whim guide the choices of many people.

For Ms. Michaels, childhood impressions trump absolution from the F.D.A.

She even carries in her purse packets of her sweetener of choice — sucralose, sold as Splenda — for those occasions when a restaurant has run out of it and she might otherwise confront a choice between pink and blue. “I’m a yellow girl,” she said.

Hundreds of millions of people swallow food and drinks containing artificial sweeteners, and so far, no widespread calamities of health have swept over them.

The F.D.A. places the three main artificial sweeteners available today in the same category: “generally recognized as safe.” The manufacturers cite multitudes of health studies to back up that assertion.

“Based on conventional food safety considerations, the scientific community feels that these have been very adequately tested for any potential toxicities,” said Dr. Gary M. Williams, a professor of pathology at New York Medical College who has been involved in safety reviews of artificial sweeteners, some financed by the manufacturers. “I drink dietsoda. I don’t need the calories. My favorite is Fresca, and actually I don’t know what’s in it.”

Part of Dr. Williams’s confidence about safety is that the artificial sweeteners are much more intensely sweet than sugar, so people consume very little of them. Most of the white stuff in the packets is filler, not sweetener. Safety tests in animals looked at doses that were hundreds or thousands of times higher.

But critics — particularly of aspartame, sold as Equal or NutraSweet — say that health problems like headaches, neurological disorders and cancers are occurring, but that regulators are ignoring them.

The Center for Science in the Public Interest, a health advocacy group, slaps an “avoid” label on saccharin and aspartame, but deems sucralose and neotame — a newer, more intense sweetener that is chemically similar to aspartame — to be safe. The center also warns against acesulfame potassium, a less common sweetener that is rarely found in tabletop packets but is combined with other sweeteners in soda and baked goods for a more sugarlike taste. Dr. Williams’s favorite soda, Fresca, for example, is sweetened with acesulfame potassium and aspartame, as are Halls sugar-free cough drops.

For those who turn to stevia, a sweetener derived from a plant, the center gives it a “caution,” because cancer studies were conducted in only one species of lab animals. (“Just because a substance is natural does not mean that it is safe,” the center’s Web site warns.)

A Google search instantly turns up worries that many have about the various sweeteners: Does NutraSweet cause brain cancer? Is Splenda really in the same chemical family as DDT? What about the studies that suggest that artificial sweeteners, despite their dearth of calories, cause weight gain?

Dr. Walter Willett, chairman of the nutrition department at the Harvard School of Public Health, says people can make rational decisions, taking into account risks and uncertainty. “The world is almost never black and white, and we rarely operate with absolute certainty about anything,” he said. “What is most important is to avoid risks that are large and clear, likesmoking, obesity and regular consumption of full-strength soda.”

Chemical Concerns

Saccharin, aspartame, sucralose and acesulfame potassium are all molecules that sidle up to certain proteins on the surface of the tongues, tickling neurons that then send a signal that exclaims to the brain: “Sweet!”

The concerns arise over what happens to the artificial sweeteners after they are swallowed.

Consider aspartame. It is essentially two amino acids and a molecular snippet known as a methyl ester. Certain people — about 1 in 25,000 in the United States — have a genetic condition that prevents them from metabolizing one of the amino acids, phenylalanine, and those people are warned away from aspartame.

Many foods contain the same two amino acids, in higher quantities. “It’s not like these are totally foreign, unique substances,” Dr. Willett said. “It doesn’t absolutely prove they’re harmless, but it makes it less likely that there’s a huge surprise waiting for us.”

Others look at the same components of aspartame and see poisons. The two amino acids, while essential for the human diet, cause problems when present out of balance, they say.

The third part, the methyl ester, turns into methanol, which is a poison — though fruit juices have higher concentrations of methanol. Woodrow C. Monte, emeritus professor of nutrition at the University of Arizona,ascribes a host of ills, including multiple sclerosis, to low-level methanol poisoning.

The scientific literature contains findings that can alarm or reassure. A huge study at a cancer research institute in Italy found that rats given aspartame had higher rates of leukemia and lymphomas. The National Cancer Institute in Maryland, however, reviewed health data from a half a million retirees and found no correlation between beverages with aspartame and these cancers.

Meanwhile, sucralose, as the Splenda manufacturer, McNeil Nutritionals, notes in its advertising, starts out as sugar. Chemical reactions excise bits of the sugar molecules and replace them with chlorine atoms. The chlorine effectively camouflages the molecules, and most pass through the body undigested. Hence, zero calories. But some wonder if the chlorine in the sucralose molecules that are absorbed by the body might cause a problem. Michael F. Jacobson, the executive director of the Center for Science in the Public Interest, said the animal testing of sucralose was sufficient for a “safe” rating.

The durability of sucralose molecules gives rise to a different concern. Measurable levels of sucralose have been found in the water supply, raising questions about what happens to various animals when they consume it.

Weighing the Risks

With the questions about artificial sweeteners, some may even wonder: How bad is sugar, anyway?

White sugar offers the purest taste of sweetness. It is natural. But its deleterious health effects are the best established: It can make you fatter.

Research published last year that analyzed health data on more than 100,000 nurses in the United States over nearly a quarter-century found a strong correlation between weight gain and consumption of sugar-sweetened beverages and desserts. There was no weight gain for those who drank beverages with artificial sweeteners.

Obesity leads to numerous health problems — diabetes, heart disease, even cancer. Sugary drinks like soda (fruit juices, too) particularly contribute to weight gain. Usually, if the diet changes, hunger signals adjust to ensure proper nutrition. But the human digestive system seems to overlook liquid calories. Someone who drinks the 140 calories in a 12-ounce can of Coke will not subconsciously eliminate 140 calories elsewhere in the diet.

“Liquid calories seem to be different, and that’s why they’re so problematic,” Dr. Willett said. “Many foods contribute to weight gain, but it does appear that sugar-sweetened beverages are the single, by far, most important problem.” (That reasoning led to Mayor Michael R. Bloomberg’s proposal to ban the sale of large sugary sodas in New York City while allowing mega-size diet sodas.)

Dr. Willett said the long-term safety of the artificial sweeteners remained an open question. “It’s interesting to keep in mind, if you smoke cigarettes, the lung cancer risk doesn’t go up for 30 years,” he said. “And that’s a really powerful carcinogen. A lot of things don’t show up for several decades.”

He also noted that trans fats, used since 1900, did not show up on the radar of doctors’ concerns until the 1990s. “It took us about 90 years to discover it was a big problem,” Dr. Willett said. “It’s a bit sobering how long that took.”

In terms of relative risk — the known dangers of sugar and weight gain versus the uncertainties of artificial sweeteners — “artificially sweetened beverages are much less bad than the full-sugar beverages,” Dr. Willett said. Still, diet sodas are less than optimal. “I view them like a nicotinepatch,” he said.

The better solution to protect health: Eat and drink less sweet stuff.

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Read the related article: “Artificial Sweeteners: The Challenges of Tricking the Taste Buds.”

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This post has been revised to reflect the following correction:

Correction: June 11, 2012

An earlier version of this article incorrectly described the composition of aspartame. An aspartame molecule essentially consists of two amino acids and a molecular snippet known as a methyl ester at one end; the methyl ester does not connect the two amino acids.