Very-Low-Carb, Ketogenic Diets
Very-low-carb diets typically induce mild to moderate ketosis, a state in which your body uses ketones and fat, rather than sugar, as its main energy sources.
Ketosis usually occurs at daily intakes of less than 50 grams of total carbs, or 30 grams of digestible carbs (total carbs minus fiber). This would be no more than 10% of calories on a 2,000-calorie diet.
Very-low-carb, ketogenic diets have been around for many years. Indeed, doctors prescribed them for people with diabetes before insulin was discovered in 1921 (5).
Several studies have shown that restricting carb intake to 20–50 grams of carbs per day can significantly reduce blood sugar levels, promote weight loss and improve heart health markers in people with diabetes (6, 7, 8, 9, 10, 11, 12, 13, 14, 15).
In addition, these improvements often occur very quickly.
For instance, in a study of obese people with diabetes, limiting carbs to 21 grams per day led to a spontaneous decrease in calorie intake, lower blood sugar levels and a 75% increase in insulin sensitivity in two weeks (14).
In a small, three-month study, people were randomized to consume a calorie-restricted, low-fat diet or a low-carb diet containing up to 50 grams of carbs per day.
The low-carb group had an average decrease in HbA1c of 0.6% and lost over twice as much weight as the low-fat group. Also, 44% of the low-carb group discontinued at least one diabetes medication, compared to 11% of the low-fat group (15).
In fact, in several studies, insulin and other diabetes medications have been reduced or discontinued due to improvements in blood sugar control (6, 8, 10, 11, 13, 15).
Diets containing 20–50 grams of carbs have also been shown to lower blood sugar levels and reduce the risk of disease in people with prediabetes (15, 16, 17).
In a small, 12-week study of obese, prediabetic men who followed a Mediterranean diet limited to 30 grams of carbs per day, fasting blood sugar dropped to 90 mg/dL (5 mmol/L), on average, which is well within the normal range (17).
In addition, the men lost an impressive 32 pounds (14.5 kg) and experienced significant reductions in triglycerides, cholesterol and blood pressure, among other beneficial health effects (17).
Importantly, these men no longer met the criteria for metabolic syndrome due to reductions in blood sugar, weight and other health markers.
Although concerns have been raised that higher protein intake on low-carb diets may lead to kidney problems, a recent 12-month study found that very low carb intake did not increase the risk of kidney disease (18).