Using your brain to eat better

Why do we feel full at the end of a meal and lose interest in eating more food? Most of us assume we experience fullness when there’s no more room left in the stomach for food. Researchers beg to differ.

As it turns out, the stomach is rarely full after a meal and our loss of interest in eating actually doesn’t come from the stomach: it comes from the brain. As a meal progresses, receptors in your stomach and small intestine detect the volume and chemical composition of what you ate and transmit that information to your brain. Your brain integrates this information into a fullness signal that gradually builds with each additional bite. When this signal has built up sufficiently, it causes you to lose interest in eating more food, a state we call satiety.

The system of gut-brain communication that governs satiety doesn’t do a perfect job of transmitting the caloric value of a meal to the brain. In other words, some foods make us feel more full than others, even if they contain the same number of calories. This means we can exploit the quirks of the satiety system naturally to help reduce (or increase) our calorie intake without discomfort. This process is particularly important as we head into the holiday season, which accounts for more than half of annual weight gain in the United States.

What foods trigger satiety the most?

In 1995 Susanna Holt and colleagues published a groundbreaking paper that gives us powerful insight into how we can use food to “trick” the brain into feeling full with fewer calories. The idea behind the trick is quite simple.

Holt and her team recruited volunteers and fed them 240-calorie portions of 38 common foods, such as bread, oatmeal, beef, doughnuts, peanuts, candy and grapes. Volunteers recorded how full they felt every 15 minutes for two hours and Holt’s team used the resulting data to calculate a “satiety index” for each food — how filling it is per calorie.

Remarkably, the researchers found that foods of identical calorie content “differ greatly in their satiating capacities.” Fat-rich bakery items, such as cake, croissants and doughnuts, had the lowest satiety index of all foods tested, meaning they deliver little satiety per calorie. White bread also fared poorly. Whole-grain bread and oatmeal, in contrast, had a significantly higher satiety index.

Fresh fruit, meat and beans tended to have a high satiety index. Plain potatoes were off the charts, more filling than any other food. Holt and colleagues noted that “simple ‘whole’ foods such as the fruits, potatoes, steak and fish were the most satiating of all foods tested.”

Calorie density

Holt’s team found that the sating ability of each item was explained largely by a few simple food properties. The first is calorie density, the number of calories per weight of food. We often call a food “rich” if it has a high calorie density. For example, oatmeal is mostly water so it has a much lower calorie density than whole grain crackers, which are similar nutritionally but contain little water.

In Holt’s experiment, the lower the calorie density of the food, the more satiety it produced per unit calorie — and the effect was robust. This result makes sense because stretch receptors in the stomach are a key signal the brain monitors to regulate satiety, and foods with a lower calorie density stretch the stomach more per unit calorie.

Palatability

Neck-and-neck with calorie density was palatability, or the pleasure value of a food. The more palatable a food, the less filling it was. Again, this makes sense. Palatable foods are those that the brain intuitively values, and the brain is good at removing barriers to getting what it wants. This is part of the reason why we tend to overeat delicious foods and magically grow a “second stomach” for dessert.

The most effective way to increase the calorie density of a food — and a very effective way to make it more palatable — is to add fat to it. This is because fat is much more dense in calories than carbohydrate and protein (9, 4 and 4 calories per gram, respectively). Not surprisingly, high-fat foods tended to have a lower satiety index.

Research shows that the reason fat sometimes makes us eat more is precisely because of its high calorie density and palatability. When fat-containing foods aren’t calorie-dense or highly palatable, they provide the same level of satiety per calorie as high-carbohydrate foods.

What this means is that if we eat fat in unrefined, filling foods, such as unsweetened yogurt, meat, fish, eggs and avocados, a higher fat intake can be compatible with a naturally slimming diet pattern. While these foods can be high in fat, they don’t have the deadly combination of calorie density and extreme palatability that characterize other high-fat foods, such as potato chips and cookies.

Fiber

Another key factor that Holt’s team identified is fiber. The more fiber a food contained, the more filling it was. This explains why whole-grain bread is more filling than white bread, despite their similar calorie density.

Finally, the protein content of a food was a major contributor to satiety. This is consistent with a large body of research showing that protein is more filling than carbohydrate or fat.

Why we overeat

Holt’s results go a long way toward explaining why we overeat without intending to in our daily lives. The nonconscious satiety circuits in the brain respond to specific food properties, such as food volume, protein, fiber and palatability.

Many of our modern processed foods don’t stimulate satiety circuits to the same degree as simple whole foods. These foods, such as pizza, ice cream, cake, cookies, soda and potato chips, invariably boast a combination of properties that make them less filling per calorie.

Since most people use the sensation of satiety to judge when to stop eating, those foods cause us to blow past the point where we’ve eaten enough calories to satisfy our needs — yet we don’t even realize we’ve overeaten because we don’t feel any more full at the end of the meal.

At the end, Holt and her colleagues put the pieces together for us: “The results therefore suggest that ‘modern’ Western diets which are based on highly palatable, low-fiber convenience foods are likely to be much less satiating than the diets of the past or those of less developed countries.” Fortunately, her findings also empower us to do something about it.

The most and least satisfying foods

10 most filling foods (most to least)

• Potatoes
• Fish
• Oatmeal
• Oranges
• Apples
• Whole wheat pasta
• Beef steak
• Beans
• Grapes
• Whole wheat bread

10 least filling foods (least to most)

• Croissants
• Cake
• Doughnuts
• Candy bars
• Peanuts
• Yogurt (low-fat sweetened)
• Potato chips
• Ice cream
• White bread
• Muesli

Sources:

1. Guyenet SJ, Schwartz MW. Regulation of Food Intake, Energy Balance, and Body Fat Mass: Implications for the Pathogenesis and Treatment of Obesity. J Clin Endocrinol Metab. 2012 Mar;97(3):745–55.
2. Holt SH, Miller JC, Petocz P, Farmakalidis E. A satiety index of common foods. Eur J Clin Nutr. 1995 Sep;49(9):675–90.
3. Rolls BJ. The role of energy density in the overconsumption of fat. J Nutr. 2000 Feb;130(2S Suppl):268S–271S.

This article was excerpted from THE HUNGRY BRAIN: Outsmarting the Instincts That Make Us Overeat. Copyright © 2017 by Stephan J. Guyenet, Ph.D. Excerpted by permission of Flatiron Books, a division of Macmillan Publishers. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.