Myth 2: For weight loss and management, a low-carbohydrate diet is the best option
The rationale for use of a low-carbohydrate diet for weight loss is that with carbohydrate restriction, fuel sources shift from glucose and fatty acids to fatty acids and ketones, leading to appetite restriction, weight loss, and improvements in risk markers for cardiovascular disease.13
However, a meta-analysis of randomized controlled trials (five trials, 447 subjects) examined the effects of low-carbohydrate versus low-fat diets on weight loss and cardiovascular risk factors in overweight and obese adults.14
After six months, individuals in the low-carbohydrate diet group had lost more weight (-3.3 kg) than those in the low-fat diet group. But at 12 months, weight loss was the same.
Changes in blood pressure were not different between groups. Whereas, total cholesterol and LDL-cholesterol decreased more in the low-fat diet group, HDL-cholesterol and triglycerides changed more favorably in the low-carbohydrate diet group. Thus, neither diet showed a clear benefit on cardiovascular risk factors.
A systematic review of weight loss studies in overweight or obese adults with type 2 diabetes with a duration of one-year or longer and a completion rate of ≥70 was conducted.15 Eleven studies met these criteria with five of the 11 studies comparing different macronutrient percentages.
One study compared a high monounsaturated fat diet to a high carbohydrate diet, two compared a low carbohydrate diet to a low fat diet, and two compared a high protein diet to a high carbohydrate diet. Regardless of the macronutrient composition of the diet, weight loss at one year was not significantly different between the groups, ranging from 1.9 to 4.0 kg.
The group with the smallest amount of amount of weight loss was a low carbohydrate diet study group which had a weight loss of 1.9 kg.16 Furthermore, eight of the groups reported nonsignificant changes in HbA1C from baseline to study end; only two groups (a high protein and a high carbohydrate group in one study) reported a modest improvement in HbA1C levels at one year.17
These studies support a conclusion that, for patients with diabetes, a variety of reduced energy eating patterns with differing macronutrient percentages are modestly effective for weight loss but may not improve HbA1C levels.
Bottom Line: For weight loss and management, patients diagnosed with diabetes are best advised to eat a reduced energy eating pattern with healthy carbohydrate foods in appropriate portion sizes.