A new study published in the journal Obesity Reviews looked at whether there's evidence to support claims that low-carbohydrate diets can also suppress your appetite, even when they severely restrict your caloric intake.
If you've given your Atkins-loving aunt the side eye, you might want to listen up.
The review of more than a dozen studies of these kinds of diets found that in most cases, participants reported feeling fuller and less hungry even while losing fat.
“We had an increase in satiety and a reduction in hunger. Both point to a reduction in appetite,” said Alice Gibson, lead author of the study and a dietitian and PhD candidate at the University of Sydney Medical School.
Researchers looked at two types of diets, both of which included low carbohydrate intake.
One type, which is similar to the popular Atkins diet, restricts carbs to fewer than 20 grams a day in certain stages – which is extremely low – but it doesn't really restrict anything else. That kind of diet is high in protein and often high in fat, but it also generally eliminates some food groups that nutritionists would recommend as part of a healthy diet, like whole grains, fruits and some vegetables.
Another type of low-carb diet – "very-low-energy diets" – similarly restricts carbohydrates. But that diet also severely restricts calorie consumption to about 800 kcals a day, far below what nutritionists would recommend as the minimum amount of energy from food that adults should consume.
"It's essentially a semi-starvation diet," Gibson said.
Those "very-low-energy diets" should really only be done under the supervision of a doctor. They also may involve carefully crafted, prepackaged meals that are designed to meet specific nutrition needs to prevent nutritional deficits caused by severely restricted calorie consumption.
After analyzing over a dozen studies, researchers saw a surprisingly consistent finding: Both types of low-carb dieters reported feeling less hungry and more full.
"All of our studies basically showed either a very small reduction in appetite or no change," said Gibson. "People can be consuming very few calories but not have an increase in their appetite."
Usually, when your body is deprived of energy in the form of food (specifically carbohydrates, which is the most efficient form of fuel), it responds by doing just what you might expect: It gives you the urge to eat by making you feel hungry.
But consuming less food and expending more energy are exactly what you're trying to do in order to lose fat. The result is often the uncomfortable, demoralizing feeling of persistent hunger. Or "hanger," when your hunger gets mixed with a little anger.
Cravings and hunger -- not to mention your bad mood -- can quickly sabotage a diet.
On low-carbohydrate eating plans, weight loss usually occurs fairly rapidly at the beginning because instead of using calories from food as fuel, the body uses fat instead. After a few days of low carbohydrate intake, the body starts to release more ketones. Often, people on ketogenic diets also report feeling less hungry, as well.
"Most people would assume that it’s their high protein intake that is causing this appetite suppression," said Gibson. "That may be contributing, but it doesn't provide an explanation for the low-energy diets, which are actually very low in protein."
Ketosis might provide a better explanation, Gibson hypothesizes. It is still unknown exactly how ketones might work to suppress appetite. But according to Gibson's research, the association between ketogenic diets and reduced or stable appetite was remarkably consistent among the studies that measured appetite before and during the diet.
The studies also suggested that even moderately restricting carbohydrates can produce a similar effect.
Some low-carb diets call for severe restrictions of fewer than 20 grams of carbohydrates a day, which generally requires cutting out healthful foods that are usually recommended as part of a balanced diet. But elevated ketone levels were still observed in study participants who consumed about 50 grams of carbs a day, which is a low, but not extreme, level of restriction.
“What I believe is that there is a threshold affect for the appetite suppression effects of ketosis,” Gibson said. “You don’t need to restrict carbohydrates to less than 20 grams.”
But appetite, at least how it is measured in most studies, is a subjective thing. And ketosis might not fully explain why some people who used low-carbohydrate diets also reported that they felt like they wanted to eat less food in general whether they were hungry or not.
"It's not clear whether it’s the ketosis or the fact that people are losing weight quickly, which is very motivating. That could also contribute the lessened desire to eat," Gibson said.
Further research is needed to investigate what happens to ketone levels at different levels of carbohydrate consumption, and also whether the appetite suppression effect effect is long-lasting.
Another study this year found that a low-carb diet resulted in more weight loss compared to a low-fat diet; but in the long run, people who followed both diets had a hard time sticking with it.
After all, you may not be quite as hungry, but giving up your favorite sandwich or pasta is no easy task, either.