Calorie deficit 101

What it is and how it works
Published July 7, 2021

You’ve heard the whole calories in, calories out thing before, but if you’ve ever wondered how it works or if it’s sustainable for the long term – here’s an explainer.

What is it

“Quite simply, a calorie deficit means that calories consumed are less than calories burned,” explains Glenn Gaesser, PhD, a professor in the College of Health Solutions at Arizona State University whose research focuses on the effects of exercise and diet on cardiovascular fitness and health. “This can be achieved by increasing calories burned (by exercise), decreasing calories consumed (dieting), or a combination of both. If a calorie deficit is sustained, weight loss will occur. There are caveats, however.”

The downsides to the theory

Gaesser explains that the calorie deficit theory isn’t perfect.

“One major hole in the calorie deficit theory is that daily energy expenditure decreases when someone creates a calorie deficit, whether by dieting or exercise. This is referred to as ‘metabolic adaptation’ or ‘adaptive thermogenesis.’ Research has shown that metabolic rate (resting and non-resting) decreases during calorie deficit. The degree of metabolic adaptation varies tremendously from person to person. Some people will have success with a calorie deficit (small metabolic adaptation), while others will have a great deal of difficulty losing weight during a calorie deficit.”

These differences between individuals, he says, are largely inherent, meaning they’re determined by our genes.

“The human body tries to defend its set-point weight (or, more accurately, set-point range). Big calorie deficits are generally countered by large metabolic adaptations, that do not generally wane with time. This explains why weight loss is transitory for most.”

Another point to keep in mind when it comes to calorie deficits is that not all calories are created equally.

Why all calories aren’t the same

Although technically, “a calorie is a calorie is a calorie,” as Gaesser says, the nutritional value of calories differs depending on the food they come from.

Registered dietitian Kristin Gillespie, MS, RD, LD, CNSC, explains.

“Two hundred calories’ worth of potato chips is not the same as 200 calories’ worth of fruit; the chips are considered empty calories and contain minimal nutrients, whereas the fruit is rich in fibre, antioxidants, and vitamins/minerals that the body needs,” she says. “Additionally, fruit and other nutrient-dense foods will keep you feeling full for longer periods of time as opposed to empty-calorie foods, which will leave you feeling hungry only a short time later and result in increased intake.”

WW’s SmartPoints system accounts for that discrepancy. Caloric values establish the baseline for every SmartPoints value, protein lowers the value while sugar and saturated fats increase the value. This is all rooted in vast research that shows the benefits of eating less sugar and saturated fat, and more protein, for weight loss and other health effects.

Other things to keep in mind

Maintain a healthy approach: “When counting calories, it is important to have a healthy approach and develop a healthy relationship with food/calories,” Gillespie says. “Focusing on low-calorie foods, such as fruits and veggies, is beneficial as it will allow you larger volumes of food and avoid feelings of restriction. Also, setting low goals for weight loss (i.e. 0.5-1 pound per week) and achievable food-related goals (i.e. simply cutting out soda to start) can help minimize feelings of significant restriction and help keep you feeling motivated and successful; setting unrealistic goals can result in feelings of defeat when you don’t achieve them.”

Focus on lifestyle for the long term: “Calorie deficits work in the short term, but generally cannot be sustained,” says Gaesser. “This can lead [to] weight regain, which is frustrating. Rather than focus on a weight-loss goal, it is probably better to make lifestyle changes that can be maintained. A little more exercise, and healthier food choices. This will likely create a calorie deficit, even if only modest. If weight loss occurs, fine. If not, don’t get discouraged. Exercise and healthy eating have their own intrinsic rewards, and should not be considered as just [a] means to an end (weight loss).”