One of the most common sayings in nutrition and fitness is: “calories in, calories out.” That means if you want to lose or maintain weight, you need to take in fewer calories than you expend.
That simple strategy tends to result in weight loss for many people, especially if there’s a large cut, according to Mike Israetel, PhD, chief sport scientist and co-founder of Renaissance Periodization, as well as a nutrition consultant for the U.S. Olympic weightlifting team.
But, he adds, it’s more complicated than it seems. There are a couple persistent misconceptions that can sabotage calorie-tracking efforts:
If you cut calories, it’s likely you’ll lose weight. But how much will you lose in a week? How about a month? Israetel says it’s a myth that using a formula like, “a 3,500-calorie deficit will result in the loss of a pound of tissue in X amount of time” will get you an exact answer. So, if you’re not “on track” and losing weight according to the formula you’re using, it’s very possible it’s not your fault.
There are a couple reasons such formulas fail to predict weight loss precisely, he says.
“First, even the formula itself is a gross generalization of physiology, and not all estimates under all conditions yield the 3,500-calories-per-pound figure, so we already have a precision error from the start,” he says.
Second, the amount of food you cut from your diet can be pretty precise, but your activity will never be as well tracked, he adds. In addition to workouts, you might be running errands one day and more sedentary the next, making it challenging to track real expenditure. So, while food input can be tightly controlled, output cannot, and you might burn way more or way fewer calories than you plan.
Finally, metabolism slows as calorie reduction continues, so you burn fewer calories the longer you make the attempt.
The better solution is to make plenty of adjustments over time based on loss of one pound a week, says Dr. Israetel.
He suggests cutting calories by 500 for each day in the first week of a calorie-reduction plan, then adjust your calories as needed in each week thereafter to keep losing about one pound per week — cutting more if you’re behind schedule and waiting to cut more if you’re on track or ahead. That way, you have a realistic goal, and you can make calorie consumption more variable based on the results you’re seeing.
Not every calorie is created equal, and each food has a specific effect on your body, according to Paul Salter, a registered dietitian and sports nutrition consultant for Renaissance Periodization.
“Each nutrient needs to be digested, absorbed and distributed,” he says. “This process requires energy — this is referred to as a nutrient’s thermic effect of food.” He notes that protein, for example, has a higher thermic effect than carbohydrates or fat.
If you eat 100 calories from protein, 20–35 calories are expended to digest, absorb and distribute that nutrient. With 100 calories from carbs, about 5–15 calories are expended.
That’s part of the reason Salter often recommends a high-protein diet to clients looking to lose weight — it helps to burn more calories, and also stimulates the release of several appetite-suppressing hormones.
The difference in how the body reacts to the type of calories can be seen in a small study done nearly 20 years ago, with results that still hold up, says Joyce Faraj, PhD, a nutritionist at Mountainside Treatment Center.
In the study, participants were split into three groups for breakfast, with options that contained the same number of calories. The first had instant oatmeal, the second had steel-cut oatmeal — which is a slow-acting carb, unlike the fast-acting instant kind — and the third had a vegetable and egg omelet with fruit on the side.
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An hour after the meal, participants in the first group had lower blood glucose levels, which Faraj says can provoke hunger and cause more eating. Tracking subsequent food intake during the day, researchers found that third group ate substantially less than the other two groups. Faraj says that’s likely because the meal had more protein and fat, which helped with satiation. So, even though the calorie counts may have been the same for all three meals, the effects were very different.
“The type of calories we choose to eat are a better predictor of how fueled up we will be, how hungry we will get throughout the day, and therefore, how much food we will end up eating,” says Dr. Faraj.
Eating foods that are nutrient dense and contain more protein, fat and slow-acting carbs helps us feel satisfied for longer, she notes, and that can lead to better success with weight management than simple calorie tracking.