In part one of this mini-series on repetitive eating patterns, I discussed findings from observational studies. While useful, observational studies do not show “cause and effect”. So in this installment, I will discuss findings from some experimental studies that have manipulated food variety and variability to show that food variety does indeed alter the amount we eat.
Part Two: Experimental Evidence
The first study I’ll describe was conducted by Professor Leonard Epstein and colleagues. Epstein has been studying obesity and determinants of food intake for over 25 years. He has hundreds of publications to his name, and his papers have been cited by others over 25,000 times. The experiment was designed to study short term habituation to food in children. Habituation is basically becoming desensitized to a stimulus despite all your senses working fine - or in other words the process of becoming bored with something. The results showed when children became bored with performing simple tasks for compensation in the form of a cheeseburger, their motivation immediately returned when the compensation was changed to apple pie . In a follow-up study Epstein and colleagues performed a study designed to see just how food-specific boredom to food may be. In this study, the researchers used macaroni and cheese to “fatigue” the children and then offered either spiral macaroni and cheese or chicken nuggets . The children recovered their motivation when offered either the spiral mac and cheese or the chicken nuggets. When offered more regular mac and cheese, the kids only consumed an additional 30 calories compared to 100 for spiral macaroni and cheese and about 150 for the chicken nuggets.
The interpretation of this study was essentially that a food stimulus only needs to be slightly different to serve as a new motivator to eat. For example, if someone ate a lunch of only beef tacos, they may have less overall motivation to eat than if they were offered a lunch with variety, like a beef taco, fish taco, and a chicken taco. This is because each taco offers a unique sensory stimulus just by changing up the type of meat. Now imagine some of the other fillings were slightly modified in each taco (as you would expect in most restaurants) and served with chips, salsa and guacamole, and a caloric beverage! I think these findings all make sense intuitively for anyone who has ever stuffed themselves at a buffet or potluck. Taken together, these findings suggest variety can delay habituation (boredom) in the short term. But how does food variety impact habituation long term?
In a study designed to investigate long term habituation to a meal, 16 obese and 16 non-obese, pre-menopausal women were fed macaroni and cheese in an experimentally controlled manner . In this study the researchers wanted to see how habituation (or boredom with a food) would be affected by feeding the meal every day for five days or once a week for five weeks. The women in this study were randomly assigned to the two groups. I’ll point out the importance of this below. The hypothesis was that the group exposed to mac n' cheese every day for five days would become bored with it, while the group receiving the mac and cheese once a week would not.
The trends in the obese and normal weight women were similar, so the data were combined in the final analyses to simplify the comparison to everyday mac n cheese eaters vs once a week mac n' cheese eaters. As expected, the daily mac n' cheese eating group experienced faster habituation, and more importantly, consumed fewer calories over time (i.e. less calories eaten on Friday vs Monday). The weekly group trended towards eating more mac and cheese as time progressed. This study did present one important caveat. The study was relatively small and the participants were randomized so the data shook out kind of funky. The group that was randomized to daily ate more initially than weekly group. The daily group started out eating about 450 calories and by the fifth day reduced calories to about 350. The weekly group started out eating 360 calories and finished out at about 400 calories. This essentially means the law of initial values may have been at play. One might argue the everyday group only decreased the amount the ate because they started out at a higher value. Nonetheless this study presents some promising preliminary data.
Previous studies indicate men are even more susceptible to eating food for pleasure (vs true hunger)  so it would be interesting to see if habituation through less variety is a more powerful tool to reduce food intake in men in future studies. The authors speculate that habituation may be applicable in the real world and that repetitive eating (same food for a given meal every day) could be an effective means to reduce food intake vs self-regulation (for example choosing salad over pizza).*
The effect of reducing food variety in weight loss interventions is not as well studied. In an 18-month weight loss intervention study, participants were instructed to limit variety of junk foods (e.g. ice cream, fries, dessert cakes) vs regular caloric reduction counseling . Both interventions involved 48 group sessions where participants were counseled on dietary choices. The group assigned to a lower variety of junk food reported that they ate less variety from junk foods at 6 months, 12 months and 18 months. Based on their reporting, they also consumed less total calories at 6 months, but they did not differ from the traditional dietary counseling group in weight loss at the end of the 18 months. Both groups lost around 10% of their initial body weight. There were no differences between groups in physical activity, although both groups increased physical activity during the intervention. Initial weights were not reported but BMIs were similar (see BMI here if not familiar), so initial weights likely were not very different. I mention this because if initial weights were different, losing a given percent of body weight could have been harder for one group vs the other. But this does not appear to be the case. While these findings to do not support the role of limited variety, you have to take self-reported dietary intake with a grain of salt. Participants are generally not very accurate in their reporting. In addition, while limiting junk food variety is a step in the right direction, there are still plenty of other foods from which variety can lead to overeating. Lastly, I’ll discuss studies on variety using animal models. These studies may be less applicable to humans than the ones reviewed so far but they do show the importance of variety in a tightly controlled setting.
A traditional model to study the effects of variety and hyperpalatable foods in rodents is the cafeteria diet. Often times rodent studies will use monotonous, high fat chows in rodent models of diet-induced obesity. However, the cafeteria diet is more similar to high fat diets consumed by humans, including high-salt, high-fat, low-fiber, and energy dense foods like cookies, candy bars, chips, and processed meats. Several studies have shown rodents eat more calories when given the cafeteria diet compared to rodents fed more monotonous diets consisting of standard or high fat-formulated chows [6, 7]. Furthermore, one study found “…rats' motivation to consume palatable foods in the absence of variety, and further diminished motivation to feed when palatable foods were withdrawn and replaced with chow.” This suggests that variety may play an independent role in over consumption of food, apart from the food necessarily tasting good or being enjoyable.
Recent animal studies indicate variability (e.g. different kind of pizza or different kind of burger each day) of foods may be just as important if not more important than variety (e.g. a range of choices for one meal). What this means is that when our body can consistently sense the energy and nutrient content associated with a food it essentially “learns” how much of that food it needs and as you eat it repeatedly you lose excitement over the food. However, if there is a lot of variability associated with the food it is very challenging for the body to know how much the eat. For example, if you eat Chicago-style pepperoni pizza every day for lunch your body can “learn” overtime how much to eat. It becomes a habit. But if you switch it up all the time eating Chicago-style, New York-style, pizza chain pizza, a local thin crust, frozen pizzas, and so on, it becomes harder for you to adapt and know roughly how much pizza you need to become satisfied. This is because all these pizza choices vary drastically in calories and nutrients.
In support of this concept, a study exposed rats to three flavored diets: a low energy diet, a medium energy diet, and a high-energy diet . All the rats in the diet were rotated through the diets daily. However, in some of the rats the flavor associated with the diets were changed randomly. The rats who rotated through the diets with consistent flavor associations were able to maintain caloric consumption that would support normal weight. Rats fed the inconsistent flavor pairings displayed dysregulated energy/nutrient sensing and ate more calories. So to sum it up, variety leaves us susceptible to overeating due to delayed habituation (boredom) in a given meal. Variability of a given food (pizza, burgers, cereals, chips, etc. too many to name in our society) can also lead to over consumption. In our society we are faced with both a lot of variety and variability in food choices. In part three I will discuss some real-world cases I have read in forums and witnessed in person whereby repetitive diets helped with weight loss or body recomps and discuss practical application.
*Due to the statistical issue I noted above and the authors speculating that reduced food variety might be a good strategy to reduce to calories long-term, another group of researchers wrote in to the journal to criticize the paper . These authors argue that the data set was too small to make any speculation and they disagreed with the interpretation of the data. They bring up the valid point that if you were to feed children boring or repetitive meals in school they may simply go to a restaurant or corner store for snacks before or after school. While this is a valid argument, Dr. Epstein’s other study on variety in children I highlighted suggests that feeding children varied meals will lead to over consumption and there’s nothing to refute that they may still go out for snacks after school. As a former fat kid I can say eating one energy dense meal did not prevent me eating another later in the day. In other words, kids would be better off to eat a boring lunch of veggies, a source of carbs, and a lean protein before gorging on Cheetos and a Mountain Dew vs eating pizza and cheesy fries before gorging on Cheetos and a Mountain Dew.
Thanks to Sofie and Vik for editing the article
1. Epstein, L.H., et al., Habituation of salivation and motivated responding for food in children. Appetite, 2003. 41(3): p. 283-9.
2. Epstein, L.H., et al., What constitutes food variety? Stimulus specificity of food. Appetite, 2010. 54(1): p. 23-9.
3. Epstein, L.H., et al., Long-term habituation to food in obese and nonobese women123, in Am J Clin Nutr. 2011. p. 371-6.
4. Bolhuis, D.P., et al., Salt Promotes Passive Overconsumption of Dietary Fat in Humans. J Nutr, 2016. 146(4): p. 838-45.
5. Raynor, H.A., et al., Limiting variety in non-nutrient-dense, energy-dense foods during a lifestyle intervention: a randomized controlled trial123, in Am J Clin Nutr. 2012. p. 1305-14.
6. South, T., et al., Rats Eat a Cafeteria-Style Diet to Excess but Eat Smaller Amounts and Less Frequently when Tested with Chow, in PLoS One. 2014.
7. Sampey, B.P., et al., Cafeteria diet is a robust model of human metabolic syndrome with liver and adipose inflammation: comparison to high-fat diet. Obesity (Silver Spring), 2011. 19(6): p. 1109-17.
8. Warwick, Z.S. and S.S. Schiffman, Flavor-calorie relationships: effect on weight gain in rats. Physiol Behav, 1991. 50(3): p. 465-70.
9. Møller, P. and E.P. Köster, Variety and overeating: comments on long-term habituation to food. 2012.
Photo credits in schematic:
Thumbnail credit to metsi @ pixbay
New York style pizza photo credit to wikicommons
Healthy thin crust arugula pizza photo credit to ubik 123 @ pixabay
Chicago style pizza photo credit to wikicommons