By Roberta H. Anding, M.S., Baylor College of Medicine and Texas Children’s Hospital

Edited by Kate Findley, The Great Courses Daily

Losing or maintaining your weight doesn’t mean you have to starve yourself. Feeling full (minus the calories) is all about volume, as Professor Anding explains.

What Makes Our Stomach Feel Full?

The stomach plays a powerful role in satiating our hunger and helping us feel full. In our stomach, we don’t have a calorie sensor. We can’t say, “Okay, that was a 500-calorie meal.” 

What the stomach does have is a “volume sensor” so we can sense volume, and volume of food makes us feel full. In this age of energy bars and foods that contain a lot of calories in a small amount of food, some researchers believe that one factor contributing to the obesity epidemic is eating a lot of foods that don’t have much volume. 

We never trigger these volume receptors in our stomach to say, “I’m done. I don’t need any more food.” Thus, the challenge for us is to create more volume in our meals. 

This goal can be accomplished through foods that are high in water volume. Fruits, vegetables, soup, yogurt, and milk are 80 percent to 90 percent water, on average. These high water volume foods stretch your stomach and the volume receptors are activated, sending chemicals to your brain that induce satiety—a feeling of fullness.

How Apples Stack Up to M&Ms^®

For example, if you received five large apples and were told to eat them in one afternoon, you would probably say, “I can’t eat five large apples. That’s way too much food.” Your eyes are telling you that the volume is too great.

However, if you were given a king-size bag of M&Ms, you’d probably say, “I could eat that” if you were being honest. The truth is, the amount of calories in the bag of M&Ms and the five apples is the same. 

It’s only the volume in the two offerings of food that is different. Additionally, foods such as apples take longer to chew than, say, M&Ms.

Because you’re taking longer to eat the food and exerting more effort into the eating process, then psychologically you feel more satisfied. Eating a meal with added complexity, such as a salad, is great because it forces you to slow down even more. 

It allows you to mindfully process your food (as opposed to the mindless binging that often occurs when we are snacking and engaged in other tasks) and chew and savor your food. The effect is not just psychological but physiological—you are giving your digestive system time to absorb the food and signal to your brain that you are full.

Thus, eating foods such as fruits and vegetables, which take up larger volumes, can greatly aid in weight management as you achieve the feeling of fullness while reducing your caloric intake. As an added bonus, many of these foods are higher in vitamins and minerals than their low-volume counterparts (cookies, candy, etc.), leading to greater overall health.

This article was edited by Kate Findley, Writer for The Great Courses Daily.

Professor Roberta H. Anding is a registered dietitian and Director of Sports Nutrition and a clinical dietitian at Baylor College of Medicine and Texas Children’s Hospital. She also teaches and lectures in the Baylor College of Medicine’s Department of Pediatrics, Section of Adolescent Medicine and Sports Medicine, and in the Department of Kinesiology at Rice University. In addition, she is a registered dietitian with the American Dietetic Association and a dietitian for the Houston Texans NFL franchise.