Brain Response to Eating the Same Foods

One potential contributing factor to increasing rates of overweight and obesity is the availability and affordability of a wide range of food choices.  A variety of inexpensive fast food options provides consumers the ability to rotate restaurant selection and reduce the risk of monotony in food selection.


Animal studies demonstrate that animals provided the same types of food (or other types of rewards) tend to reduce the level of consumption.  This is a behavioral trait known as habituation.  Habituation represents the tendency to  reduce total caloric intake when eating the same foods and to increase caloric intake when presented novel food choices.


Food habituation in humans has received limited attention.  For example, it is unclear whether being presented the same food weekly results in habituation.   Additionally, it is unclear whether food habituation occurs in similar manner for those who normal weight compared to those who are overweight.

Understanding habituation in humans may provide an insight in how to use food presentation to reduce or increase caloric intake.

Epstein and colleagues recently published a simple but important study of food habituation in a group of normal weight and obese women in the American Journal of Clinical Nutrition.  The study design was relatively straightforward.  Each group of normal weight and obese women were divided in two and were studied in one of two longitudinal experiments:

• Daily group: Every day for 5 days over the lunch hour, women in this group were brought into the lab and provided an opportunity to earn a 125 calorie portion of macaroni and cheese.  Subjects could decide to persist for up to 14 portions over 28 minutes or if they elected they could leave the food station and attend to a station where a newspaper and Sudoko puzzles were available.
• Weekly group:  The weekly group performed an identical experiment except they attended once a week for five weeks

So the experiment essentially tried to determine how enticing a single food (macaroni and cheese) was when offered on a daily compared to a weekly basis.  The key results of the study were:

• Women presented daily macaroni and cheese reduced caloric consumption of mac and cheese by about 100 calories from day 1 to day 5 and reduced their rating of how much they liked mac and cheese over the course of the study
• Women presented weekly macaroni and cheese increased caloric consumption of mac and cheese by about 100 calories from week 1 to week 5
• The pattern in obese women looked identical to that found in women of normal weight

So, if you are interested in losing weight, eating the same thing daily may be a way to use the habituation process to aid calorie restriction.  However, if you eat the same thing every day you do need to worry about the nutritional profile of what you are eating.  Appetite and drive for specific foods may be a biological mechanism to assure intake of all necessary nutritional components.

This study confirms that humans, like animals develop food habituation when presented the same food daily.  Habituation does not appear to be influenced by being obese.  It is unclear why this biological process develops.  Perhaps it is a mechanism to encourage exploration for novel foods that may add nutritional diversity.

Photo of sunrise at Juno Beach, Florida from author's collection.

Epstein LH, Carr KA, Cavanaugh MD, Paluch RA, & Bouton ME (2011). Long-term habituation to food in obese and nonobese women. The American journal of clinical nutrition, 94 (2), 371-6 PMID: 21593492

Exercise May Reduce Appetite But Increases Calorie Consumption

The relationship between exercise, appetite and food intake is a complex relationship.  Aerobic exercise has been touted as a way to reduce appetite potentially increasing weight loss.  This effect has been termed the anorexia of exercise.  The effect appears to be commonly found after exercising at greater than 60% of maximum oxygen consumption.  This decreased appetite after exercise has been  possibly due to the redistribution of blood flow from the gastrointestinal tract to the peripheral muscles.   However, a temporary reduction in appetite following exercise may not actually correlate with a reduced caloric consumption over a more extended period of time.

Derek Laan and colleagues from Purdue University and the University of Missouri recently published a further look at the relationship between exercise, appetite and caloric intake.  In addition to aerobic exercise, they examined the effect of resistance exercise on appetite and calorie consumption.  The key issues in the design of this study included:

• Subjects: Male and female from the Purdue community, ages 18 to 29, BMI between 18 and 29 (normal weight to overweight but obesity excluded), percent body fat less than 20% for men and less than 35% for women, not currently dieting with no recent weight loss/gain, nonsmokers, nondiabetic and exercising at least twice per week for 30 minutes in each of aerobic and resistance categories.
• Experimental Design: Three sessions: 1.) one aerobic session of 35 minutes cycling at 70% maximum heart rate, 2.) one resistance training session of 35 minutes including 3 sets of 5 weight lifting exercising at 75% maximum, 3.)  a control session of no exercise
• Appetite and Calorie Consumption:  1.) Perceived appetite rated before and after exercise using 13 point scale with 1=not at all hungry and 13=extremely hungry, 2.) Thirty minutes after exercise subjects were given 30 minutes to consume a pasta salad meal with instructions to eat as much or as little as desired until feeling comfortably full.

The key results of the research included:

• Aerobic exercise but not resistance exercise reduced hunger ratings 10 minutes after exercise.  The effect lasted about 30 minutes when hunger ratings returned to levels experience by resistance exercise and controls
• Mean caloric meal intake was 897 calories for aerobic exercise group, 924 calories for the resistance exercise group and 784 calories for the control group (both exercise groups consumed more than controls—14 to 18% more, a statistically significant amount

The authors concluded that in healthy adults, aerobic exercise does temporarily reduce hunger ratings but the effect is small, transient and not related to reduced calorie consumption in an unrestricted meal setting.  A similar study would be interesting in a group of patients with anorexia nervosa who commonly exercise to excess in an attempt to lose weight and maintain weight below medically healthy levels.   Additionally, similar studies in obese subjects might be helpful in prescribing the best exercise and diet regimens for weight loss.   This study suggests resistance training alone may increase caloric intake more than the calories expended in resistance exercise.   The increase caloric consumption with aerobic exercise probably contributes to the limited weight loss found in starting an aerobic exercise program.

Photo of March 2011 sunrise at Juno Beach, Florida courtesy of Yates Photography.

Laan DJ, Leidy HJ, Lim E, & Campbell WW (2010). Effects and reproducibility of aerobic and resistance exercise on appetite and energy intake in young, physically active adults. Applied physiology, nutrition, and metabolism = Physiologie appliquee, nutrition et metabolisme, 35 (6), 842-7 PMID: 21164556