La mayoría de las personas que hacen dieta conocen la dura verdad: seguir un régimen de pérdida de peso se vuelve más difícil a medida que pasa el día. Pero mientras que los que ceden a los antojos de alimentos y atracones de noche pueden culpar a la flagrante fuerza de voluntad, un nuevo estudio sugiere que el problema podría estar en la compleja orquesta de hormonas que impulsan el hambre y señalan sentimientos de saciedad o plenitud.

El pequeño estudio de 32 hombres y mujeres obesos, la mitad de los cuales tenían hábitos de atracones, sugiere que las hormonas de la saciedad pueden ser más bajas durante las horas de la noche, mientras que las hormonas del hambre se elevan al caer la noche y pueden ser avivadas por situaciones estresantes. Los comedores de exceso de peso pueden ser particularmente susceptibles a la influencia de las fluctuaciones en estas hormonas reguladoras del apetito, hallaron los investigadores.

“Hay más oportunidades de comer en la noche, pero este estudio muestra que las respuestas hormonales los están preparando para hacer esto”, dijo Susan Carnell, profesora asistente de psiquiatría y ciencias del comportamiento en la Facultad de Medicina de la Universidad Johns Hopkins, que fue la primera autor del estudio junto con Charlotte Grillot de Florida State University. No está claro si estos patrones hormonales preceden y provocan los comportamientos de atracones o están condicionados por los hábitos alimenticios de un individuo, dijo el Dr. Carnell. Pero de cualquier manera, “puedes quedarte atrapado en el ciclo”.

El estudio es un recordatorio importante de que una miríada de factores contribuye al aumento de peso, y que avergonzar y culpar a las personas por sus problemas de peso es inapropiado, dijo Kelly Costello Allison, directora del Centro de Trastornos del Peso y la Alimentación de la Universidad de Pennsylvania, que no involucrado en la nueva investigación.

“Hay tanto prejuicio y juicio sobre las personas que tienen sobrepeso, que es su culpa o que son vagos o simplemente no tienen suficiente fuerza de voluntad”, dijo el Dr. Allison. “La conclusión es que las personas están conectadas de diferentes maneras, y algunas de ellas realmente dependen de estos marcadores biológicos”.

The new findings were published in the International Journal of Obesity in December. They build on earlier work, including a 2013 Harvard study of normal-weight individuals that found circadian rhythms play a role in regulating appetite, and that hunger peaks in the evening and appetite is, paradoxically, at its lowest in the morning, even though people have not eaten all night.

That research helped explain why so many people skip breakfast, even as evidence mounts that consuming most of one’s calories at the beginning of the day is optimal for weight control and a healthy metabolism.

Evening hunger “may have been an evolutionary adaptation that helped us get through the night”, said Dr. Satchidananda Panda, a professor at the Salk Institute for Biological Studies in San Diego. “For millions of years, our nighttime period was a time when we didn’t have access to food, and you also could not just get yourself food as soon as you woke up in the morning”. In the modern era, with easy access to food at any time of day or night, that evolutionary adaptation may be backfiring, leading to loss of control and nighttime binges.

For the new study, participants were asked to fast for eight hours before consuming a 600-calorie liquid meal.

Then, two hours later, they were subjected to a stress-inducing situation in which they had to submerge their nondominant hand in freezing water for two minutes while they thought they were being filmed (they weren’t). Thirty minutes later, they were offered a buffet of pizza, snacks and sweets.

To gauge the impact that time of day might have on appetite and appetite-regulating hormones, the researchers put the participants through the regimen twice, once starting at 9 a.m. and once starting at 4 p.m. They took blood to measure hormone levels and also asked participants to rate their subjective feelings of hunger and fullness using a numeric scale.

All of the participants reported being hungrier if they started the regimen in the evening compared with the morning. Likewise, they had higher levels of a hormone called ghrelin that makes people hungry and lower levels of a satiety hormone, peptide YY, if they had consumed the liquid meal in the afternoon instead of the morning.

Binge eaters also showed higher initial levels of ghrelin when they started the regimen in the evening, compared to starting in the morning, while those who weren’t binge eaters had the reverse pattern. The binge eaters also reported feeling less sated after the liquid meal and the exposure to the stressor in the evening.

Stress drove up hunger in all of the participants, but the hunger hormone ghrelin rose even higher if participants were subjected to the stressful situation later in the day, suggesting stress may have a more profound effect on hunger in the evening. (There was no group for comparison that had not been subjected to the stressor, however.)

“We definitely know that this pattern of hormone responses increases the risk of overeating in the evening, as opposed to the morning”, Dr. Carnell said. “It implies the people in our study were more vulnerable to overeating in the evening”. She suggested that people who know they tend to overeat in the evening and at night make sure to set aside time to eat properly during the day and adopt an “eating curfew”, a set time in the evening when they stop eating for the day.

Dr. Allison agreed. “Set a ‘kitchen is closed’ time”, she advised. “Shut off the kitchen light, move away from the kitchen, brush your teeth, and if you want anything after that, have water”.

“At night, in particular, you’re tired, you’ve had cognitive demands to meet during the day, you’re not wanting to regulate yourself as much, and if you have food cravings, there are fewer distractions to help you resist those cravings”, she said.

Ella y otros expertos señalan que los niveles de hormonas responden a los patrones de alimentación y pueden ser reacondicionados si las personas cambian sus hábitos alimenticios. Pero incluso si eso es cierto, “se enfrentan a un obstáculo más grande, porque primero tienen que cambiar sus hábitos alimenticios y esperar a que sus hormonas del hambre se pongan al día”, dijo Courtney Peterson, profesor asistente en el departamento de ciencias de la nutrición de la Universidad de Alabama en Birmingham.

“No es que no haya esperanza para ayudar a la gente que tiene estos problemas”, dijo la Dra. Allison. “Simplemente muestra que hay diferentes puntos de partida para todos. Algunas personas tienen más desafíos que enfrentar en términos de cómo regular su ingesta de alimentos debido a estas razones biológicas “.

Créditos: The New York Times

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