A. Janet Tomiyama, PhD

A. Janet Tomiyama, PhD

Eating, obesity, and health

Broadly speaking, my work is focused on eating and obesity, looking at the different ways that the way we eat can make us unhealthy. Specifically, my research is focused around three central questions: (1) Why do we eat… (2) …when we don’t want to? (3) and is not eating really the answer?  Here, I’ll outline some examples of my research that tries to answer these questions.

Green Apple Bite

Why do we eat?

The simplest and most obvious answer is hunger, but that is NOT the end of the story. Think of the last time you had a birthday party for a co-worker, for example.  Was it hunger that caused you to accept the plate of cake? In a study of 137 females (Tomiyama, Comer, & Mann, 2009), my colleagues and I gave people PDAs to carry around with them for two days. Every hour, we asked (a) whether they ate; (b) how much they ate; and (c) what was happening before they ate.  (We also asked them a bunch of other, unrelated questions to hide our interest in eating so they wouldn’t be tempted to bend the truth.) We found that yes, hunger had a lot to do with eating, but that other things like happiness and sadness affected our eating as well. Being distracted was related to people eating less than they normally do.  Experiencing positive or negative moods was also related to eating less, but only immediately after feeling that mood. Interestingly, when we looked at their eating an hour later, we found that they tended to eat more than normal.

Eating, obesity, and health

…when we don’t want to?

Why do we eat when we don’t want to?  Here, I am interested in what happens when people go on diets.  My guess is that some of you who answered “yes” to the “have you ever been on a diet?” question didn’t manage to keep weight off. You are not alone.  In a review of scientific studies on diets (cutting calories for the purposes of weight loss), my colleagues and I looked at every single diet study that followed people for at least two years after the diet had ended. What we found was sobering – over two-thirds of participants gained back more weight than they lost initially on the diet (Mann, Tomiyama et al., 2007).

The next question was WHY.  Why don’t diets work?  A major finding in this area is called the disinhibition effect. In the study that first demonstrated this phenomenon (Herman & Mack, 1975), participants were asked to be in a “taste test” study, and were required to first drink a milkshake.  Then, they were given three flavors of ice cream to taste and told that the experimenters were trying to see whether the flavor of the milkshake affected participants’ sensory experience of the ice cream. People who weren’t dieting were full after the milkshake and didn’t eat much ice cream.  Dieters, however, ate much more of the ice cream than non-dieters. The researchers believed that once dieters think their diet is blown, they give up and binge. This sounds very intuitive and seemed like a good place for us to look as a reason why diets don’t work. But all of the studies demonstrating the disinhibition effect took place in the laboratory.  We decided to see whether this happened in real life.

We did this in two ways (Tomiyama et al., 2009).  First, we again gave people PDAs, and this time asked whether participants had violated their diet. Then we asked questions about whether and how much they ate. (Once again, we buried these questions in a bunch of unrelated questions and spaced the diet violation question far away from the eating question.) We found that breaking your diet didn’t seem to be related at all to how much you ate immediately afterward, or even in the hour after.

Unconvinced, we did a second study where we forced people to violate their diets. A group of chronic dieters participated in what they thought were two unrelated studies. In the first, they were asked to help us test new food monitoring software for user-friendliness and bugs. We simply told them to enter in all the food that they ate over the next 8 days. In the second study, run on a different day with a different experimenter in a different room, they were asked to do a bogus memory task, drink a milkshake (forcing them to blow their diet) and then do another bogus memory task. (The cover story was that we wanted to see whether food really improved memory.) We then spied on their eating through what the entered into the software for the other study to see what happened after they were forced to violate their diet. Once again – nothing. In the real world, dieters didn’t seem to be binging after breaking their diets.

Since that didn’t seem to be the answer, we next thought that perhaps diets failed because they were stressful. After all, we already know that stress can cause weight gain through many different pathways. In another study (Tomiyama et al., 2010), we randomly assigned people to diet or not diet and monitored their psychological stress levels as well as levels of the stress hormone cortisol. We also examined whether it was the cutting-calories part of dieting that might be stressful, or the counting-calories part, or maybe a combination of both.  So some people did both – they counted the caloric content of their food and cut their intake to 1200 kilocalories per day. This is what most people in the real world do when they go on a diet. Some people were randomly assigned to just count their calories via a detailed food diary. Some people were given all the food that they were to eat over the course of the study – 1200 kilocalories again, but they didn’t have to think about it or count the calories. Finally, some people were asked not to change anything about their eating. We found that people think counting calories are stressful, but when it comes to our stress hormones, only cutting calories significantly increased cortisol. This finding was important because cortisol causes us to gain weight, particularly in our belly region, and is linked to all sorts of bad health outcomes.


Is not eating really the answer?

This and other research has led me to suspect that dieting is not the answer for weight loss or better health.  However, many of researchers would say that dieting IS the answer. After all, in other species like rats, yeast, mice, flies, worms, fish, and even rhesus monkeys, caloric restriction causes lifespan to increase, sometimes by ten-fold (Heilbronn & Ravussin, 2003). In fact, caloric restriction is the only known intervention for lifespan increase. This is another paradox that I am trying to resolve during my time as a Robert Wood Johnson Foundation Health and Society Scholar.

The key may be that “caloric restriction” and “dieting” studies in humans have actually been studying yo-yo dieting. After all, dieting is hard, and hard to keep doing over long periods of time. This is a very different picture from non-human animal “dieting” studies where the experimenter has total control over how much the animals eat. In other words, the animals don’t have the option of going off their diets. What is critically necessary, therefore, is to find a human model of true caloric restriction that parallels the animal models, where low levels of caloric intake are maintained over a long time.

Luckily, there actually are people who have been doing this – sometimes for decades. They are the members of the Calorie Restriction (CR) Society – people who have used the scientific findings surrounding caloric restriction and lifespan extension and applied it to their own lives. Along with leaders in the field of caloric restriction and aging like Elizabeth Blackburn, Anne Brunet, Elissa Epel, Pankaj Kapahi, Cynthia Kenyon, Jue Lin, and Eric Verdin, and with support from RWJF Health Disparities Working Group and the Appleby Foundation, I am embarking on a study of caloric restriction in humans. Together with Paul McGlothin, VP of Research for the CR Society and Meredith Averill, Board Member of the CR Society, we are creating a collaboration to study the effects of long-term caloric restriction in humans. Specifically, we are looking at aging markers and processes that have been discovered in the animal models and seeing whether we can see the same thing in humans.

In sum, it’s clear that eating, which is an act very central to the lives of all creatures, can have an important impact on our health. My goal is to create a research career that will pinpoint how to harness the power of eating to create healthier, happier, longer lives.


Heilbronn LK, & Ravussin E. (2003). Calorie restriction and aging: review of the literature and implications for studies in humans. American Journal of Clinical Nutrition, 78, 361-369.

Herman, C.P., & Mack, D. (1975). Restrained and unrestrained eating. Journal of Personality, 43, 647–660.

Mann, T., Tomiyama, A.J., Lew, A.M., Westling, E., Chatman, J., & Samuels, B. (2007).  The search for effective obesity treatments: Should Medicare fund diets?  American Psychologist, 62, 220 – 233.

Tomiyama, A. J., Mann, T., Comer, L. (2009). Triggers of eating in everyday life.  Appetite, 52, 72-82.

Tomiyama, A. J., Mann, T., Vinas, D., Hunger, J. M., DeJager, J., & Taylor, S. E. (2010). Low calorie dieting increases cortisol. Psychosomatic Medicine.

Tomiyama, A. J., Moskovich, A., Byrne Haltom, K., Ju, T., & Mann, T. (2009). Consumption after a diet violation: Disinhibition or compensation? Psychological Science, 20(10),1275 - 1281.


A. Janet Tomiyama, PhD

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A. Janet Tomiyama, PhD