Your body needs fat to function, but having more fat stored than your body needs can have health consequences. Obesity—having an excessive amount of body fat—has long been thought to be caused by eating more than your body will use for energy.

Key Takeaways

  • Researchers propose that obesity is not as simple as the “calories in, calories out” equation for weight management.The carbohydrate-insulin model suggests that people gain weight when they consume excessive amounts of processed carbohydrates, which in turn causes insulin levels to rise and results in the body storing fat.Focusing on eating fewer processed carbohydrates (such as crackers, candies, and cakes) may help people manage their weight more effectively than just keeping track of how much they eat.

However, some experts say that obesity is likely a far more complex process and that the “calories in, calories out” theory of weight gain is an oversimplification.

The causes of the obesity epidemic in the U.S. are still being researched, but a new study published in The American Journal of Clinical Nutrition suggests that a major driving force behind it might be what we eat rather than how much we eat. 

According to the Centers for Disease Control and Prevention (CDC), obesity affects over 40% of American adults.

“Obesity is a disease, not a lack of willpower,” Lauren Harris-Pincus, MS, RDN, a New Jersey-based registered dietitian and the author of “The Protein-Packed Breakfast Club,” tells Verywell. “And it’s becoming more widely recognized that overeating doesn’t cause obesity; the disease of obesity causes overeating.”

The Health Effects of Obesity

Research has shown that carrying excessive body weight is linked to several health conditions and can increase a person’s risk for chronic diseases.

Some of the physical and mental health consequences of obesity include:

  • High blood pressure
  • Sleep apnea
  • Type 2 diabetes
  • Cardiovascular disease
  • Poor mental health and reduced quality of life

Overeating May Not Be the Cause of Obesity

Overeating energy-dense processed foods and a sedentary lifestyle is thought to be the main cause of obesity. However, because the rate of obesity has continued increasing despite this theory, researchers are now exploring whether calories from any source are contributing.

Finding effective ways to treat—or even prevent—obesity has been a mission of researchers and healthcare providers for many years.

According to Harris-Pincus, obesity is a “dysregulation of energy intake resulting from many genetic and environmental factors.”

After noting that the recommendation to eat fewer calories than the body uses (calorie deficit) has not appeared to slow the rates of obesity, researchers set out to explore how the body responds to certain foods to determine whether some foods play a more significant role in weight.

Lauren Harris-Pincus, MS, RDN

It’s becoming more widely recognized that overeating doesn’t cause obesity; the disease of obesity causes overeating.

The Carbohydrate-Inuslin Model

The researchers have theorized that obesity might result from eating excessive amounts of highly processed carbohydrate-rich foods, such as pretzels, candies, and cakes. Processed foods are lower in fiber, higher in carbohydrates, and are not as nutrient-dense as less processed foods.

Eating processed foods leads to more insulin secretion and less glucagon secretion. When this occurs, fat storage in the body can increase and ultimately cause a slower metabolism and an increased feeling of hunger.

“Too much focus on total calories leaves a huge gap where you should be thinking about an overall balanced diet,” Kacie Barnes, MCN, RDN, LD, a Dallas-based registered dietitian, tells Verywell. “Most people would find that if they ate 100 calories worth of gummy worms or 100 calories worth of a chicken breast, you will feel satisfied for longer with the chicken breast. So, not only are you less satisfied when you eat more highly processed carbohydrates, this study suggests that you also will store more fat.”

A New Approach to Obesity

Doctors have long defaulted to advising patients who need to lose weight to eat fewer calories without focusing as much on where those calories are coming from.

However, researchers are now learning that weight management is more nuanced than a calorie deficit and that the macronutrients in the foods that we consume can have different effects on our hormone levels.

Certain hormones play a role in fat storage, carbohydrate metabolism, and other factors related to energy use, which is one reason it might be helpful to shift the focus to what we are eating rather than how much.

The Role of Glycemic Index

With regard to carbohydrate type, a food’s glycemic index (GI) describes how fast it raises blood glucose (and therefore insulin) levels in the two hours after it is eaten.

Previous studies have shown that low glycemic index diets that are rich in foods that do not cause blood glucose spikes can help lower body weight.

While the authors of the new study note that more rigorous research is needed to compare the two approaches to obesity, their research suggests that focusing on low-GI foods—as opposed to simply thinking about caloric intake for all food—could be key to helping some people manage their weight.

Many refined and processed grains, as well as added sugars, digest quickly and have a relatively high GI. Non-starchy vegetables, legumes, whole fruits, and intact whole grains tend to have a moderate or low GI. 

You can work in reducing your intake of high GI foods by choosing:

  • Whole-grain crackers with peanut butter instead of pretzelsSparkling water or seltzer instead of soda/soft drinks/popWhole-grain bread instead of white breadBran flakes instead of corn flakes

Harris-Pincus says that to give yourself the “best chance at sustainable weight loss,” focus on making the base of your diet “fruits, veggies, nuts, beans, seeds, whole grains, lean proteins and heart-healthy fats like avocados and olive oil,” and eat them in “portion sizes that satisfy you.”

What This Means For You

If you are trying to manage your weight or lose weight, new research suggests that what you eat might matter more than how much you eat. To avoid blood sugar spikes that can lead to more fat storage, focus on including more low glycemic foods in your diet.