Low-carbohydrate diets or low-carb diets are dietary programs that restrict carbohydrate consumption, often for the treatment of obesity or diabetes. Foods high in easily digestible carbohydrates (e.g., sugar, bread, pasta) are limited or replaced with foods containing a higher percentage of fats and moderate protein (e.g., meat, poultry, fish, shellfish, eggs, cheese, nuts, and seeds) and other foods low in carbohydrates (e.g., most salad vegetables such as spinach, kale, chard and collards), although other vegetables and fruits (especially berries) are often allowed. The amount of carbohydrate allowed varies with different low-carbohydrate diets. Such diets are sometimes ‘ketogenic’ (i.e., they restrict carbohydrate intake sufficiently to cause ketosis). The induction phase of the Atkins diet is ketogenic.
The term “low-carbohydrate diet” is generally applied to diets that restrict carbohydrates to less than 20% of caloric intake, but can also refer to diets that simply restrict or limit carbohydrates to less than recommended proportions (generally less than 45% of total energy coming from carbohydrates).[
More effective than a low fat diet
There is accumulating evidence that a low-carbohydrate diet may help people lose weight more quickly than a low-fat diet—and may help them maintain that weight loss.
- For example, POUNDS LOST (Preventing Overweight Using Novel Dietary Strategies), a two-year head-to-head trial comparing different weight loss strategies, found that healthy diets that varied in the proportions of different macronutrients (carbohydrates, protein and fats) worked equally well in the long run, and that there was no speed advantage for one diet over another.
- The DIRECT study compared low-carb, low-fat, and Mediterranean-style diets and found that after 2 years, weight loss and maintenance were better for low-carb and Mediterranean-style diets as compared to low-fat diets.
- The diets also had different effects on heart disease risk factors.
The low-carb diet was most beneficial for lowering triglycerides, the main fat-carrying particle in the bloodstream, and also delivered the biggest boost in protective HDL cholesterol.
Lowering the risk of heart disease
Research shows that a moderately low-carbohydrate diet can help the heart, as long as protein and fat selections come from healthy sources.
- A 20-year prospective study of 82,802 women looked at the relationship between lower carbohydrate diets and heart disease; a subsequent study looked at lower carbohydrate diets and risk of diabetes. Women who ate low-carbohydrate diets that were high in vegetable sources of fat or protein had a 30 percent lower risk of heart disease and about a 20 percent lower risk of type 2 diabetes, compared to women who ate high-carbohydrate, low-fat diets. But women who ate low-carbohydrate diets that were high in animal fats or proteins did not see any such benefits.
- More evidence of the heart benefits from a lower-carbohydrate approach comes from a randomized trial known as the Optimal Macronutrient Intake Trial for Heart Health (OmniHeart). A healthy diet that replaced some carbohydrate with protein or fat did a better job of lowering blood pressure and “bad” LDL cholesterol than a healthy, higher-carbohydrate diet.
- Similarly, the small “EcoAtkins” weight loss trial compared a low-fat, high-carbohydrate vegetarian diet to a low-carbohydrate vegan diet that was high in vegetable protein and fat. While weight loss was similar on the two diets, study subjects who followed the low-carbohydrate “EcoAtkins” diet saw improvements in blood lipids and blood pressure.