New Study Tells Us What Makes Us Overeat
by Tiago Vasconcelos, RP Research Editor |
Mar 06, 2023
Why we overeat
It's not news that eating in a caloric surplus leads to weight gain, and a caloric deficit leads to weight loss. While many have tried to dispute such a fact by appealing to hormonal factors or several types of diets, the research that neither of the latter is a main driver of body weight change is overwhelming.
Still, this doesn't solve the problem of obesity. Most know they need to eat less to lose weight, but doing so consistently in practice is difficult! The true challenge is not knowing what causes weight loss but how to create a plan that enables people to adhere to a diet that produces that weight loss.
Exercise and overall physical activity are, of course, a part of this. We lead largely sedentary lives, and we need to be more active. Doing so not only massively improves our health but also improves our body composition and increases our energy requirements––meaning we can eat more without gaining.
While exercise is important, one's diet is much more important in determining weight loss, especially in the short term. The problem is that people don't tend to stick with it! They end up overeating in some way or another.
The role of hunger
One way to prevent this is to devise ways that restrict one's energy intake without necessarily having to track it. This is called "ad libitum energy intake”. Meaning the number of calories you consume without attempting any restriction.
For example, if you had 400 calories from pizza for lunch today, but tomorrow you will have 400 calories from a chicken salad instead, your natural appetite for dinner on both days will likely be very different. You will naturally be hungrier in the pizza scenario, and thus consume higher calories during dinner.
A recent study by Fazzino et al. (2023) investigated what affects this natural regulation. Using data from almost 3000 meals across 35 subjects, they looked at what makes us eat more. A great strength of this study is that this is data from controlled feedings, meaning we can know what the participants were eating with certainty. Self-reported studies, on the other hand, are notoriously unreliable. People forget what they eat, and sometimes even lie!
So, what did the study uncover? They showed that three main variables affected how many calories people ate in a single meal:
- Eating rate
- Energy density
- Hyper-palatable foods
The eating rate is how fast people eat. It was already a well-established variable for weight loss. If food is consumed slower, the entrance into the intestinal tract also decreases, affecting gut hormone response, such as a PYY and GLP1, modulating satiety (Argyrakopoulou et al., 2020). Although evidence was lacking that it had a short-term effect on subsequent meals, this newer research solidifies its importance.
Another factor was energy density - how many calories per weight a given food has. If an energy surplus causes weight gain, then not surprisingly, more calorically dense food will contribute disproportionately to that weight gain. The pizza compared to the chicken salad is a good example of this. The fewer calories per volume of food, the harder it is to overconsume.
Finally, the last contributor is hyper-palatable foods. Hyper-palatable foods is a more technical term, but its overall concept is simple: things that taste delicious. Some foods are more delicious than others. They generally tend to fall into a few predictable patterns, often in nutrient pairs: fat and sugar, fat and sodium, and carbohydrates and sodium (Fazzino et al., 2019). They have a certain range that they operate as well. For example, something can be too sweet, at which point we find it less enjoyable.
The role of protein
High protein has often been considered an important variable for satiety (Halton & Hu, 2004) and thus controlling energy intake. Yet this wasn’t supported in this study, at least fully. Protein content seemed to increase intake in some cases but not in others.
While high protein increased calorie intake with a low-fat and low-carb diet, it lowered it with a diet of ultra-processed foods. It's unclear what such results mean; honestly, it might be noise in the data or being affected by confounders. However, the fact that protein intake does not always affect satiety is not new.
Protein’s effect on satiety might be context-dependent, such as having a low protein intake. Some have argued that humans may prioritize the consumption of protein over other macronutrients until protein needs are met, called the protein leverage hypothesis (Bekelman et al., 2017; Simpsons & Raubenheimer, 2005).
A meta-analysis by Ravn et al. (2013), using 5 studies of meal-test with 111 participants, concluded that protein content does not lead to appetite suppression in meals when protein is around ~15% of energy intake or so. In this way, a typical maintenance of around 15 calories per lb would translate to 0.56g/lb.
That value lines up well with the minimum protein required for health. While the RDA is 0.36g/lb, Layman (2009) has convincingly argued that this is too low based on available evidence, and 0.54g/lb is a good target. Right now, it looks like it’s not clear yet if high protein intake has a significant effect on satiety compared to a sufficient/moderate intake. Hopefully more research will settle this point in the near future.
What's behind our overeating
Returning to the original study, the results are consistent with previous research and what we know about energy intake and weight gain. Eating rate, energy density, and hyper-palatable foods all contribute to increased energy intake, making it harder to lose weight. And the obesity epidemic is greatly influenced by these factors, which have intensified in the modern world.
Sitting down for a meal undisturbed is increasingly uncommon, likely affecting our eating rate, with TVs or smartphones being a useful distraction during our meals. Yong et al. (2021) found that during 1 week, 85% of subjects used their smartphones when eating at least once, and they used it on average in 1/3 of all meals.
Finally, energy density and hyper-palatable foods are often interconnected, and it’s an unavoidable byproduct of increasing food processing and the reduction of home cooking. Although, of course, obesity is a complex phenomenon, and many other factors play a role, such as sedentary lifestyles, lower cost of food, increased food availability and convenience, and mental health problems.
What to do about it?
This study and others like it can be insightful if you want to lose weight. The ideal goal is to reduce one's intake without having to force by pure restriction alone. Therefore, if you want to make weight loss easier, focus on the following:
- Focus on eating slower. Don't rush it. Be mindful of each bite, don't be distracted by electronics, and pay attention to satiety cues.
- Eat more foods that are low in calorie density. Not saying you can't have some delicious peanut butter! But if you want to lose weight, having a high amount of low-calorie foods like vegetables is a great idea.
- Avoid hyper-palatable foods. Such foods will likely lead to caloric overconsumption. If you can fit it into your macros, there's nothing wrong with some delicious french fries or ice cream. But it might be best not to make it a daily occurrence. Many find it hard to eat it in moderation, end up hungrier due to their caloric density, crave even more of that food, and find common healthy foods less appetizing.
Following these recommendations will pay dividends in your fat loss journey and overall better health. If you want a more structured plan with more specific guidance besides these recommendations, check out our RP Diet App. It's like a Nutrition Coach in your pocket - it tells you exactly what to eat and when! You can download it at www.rpdiet.app.