Which Diet for Type 2 Diabetes?

In a randomized crossover study of 13 participants with T2DM, the Paleolithic diet improved glucose control and several cardiovascular disease markers, compared to a standard diabetes diet. The Paleolithic diet resulted in significantly lower A1C, triglycerides, diastolic blood pressure, body weight, BMI, and waist circumference, as well as increased HDL. Despite receiving no instruction to restrict calories, patients on the Paleolithic diet consumed fewer calories and carbohydrates, and more protein and fat, than those on the standard diabetes diet. The caloric deficit accounted almost exactly for the observed difference in weight loss between the two groups.⁹

GLYCEMIC INDEX

The GI measures the blood glucose level increase in the two hours after eating a particular food, with 100 representing the effect of glucose consumption. Low-GI food sources include beans, peas, lentils, pasta, pumpernickel bread, bulgur, parboiled rice, barley, and oats, while high-GI foods include potatoes, wheat flour, white bread, most breakfast cereals, and rice.

A meta-analysis compared the effects of high- and low-GI diets on glycemic control in 356 patients with diabetes. Ten of 14 studies documented improvements in A1C and postprandial plasma glucose with lower GI diets. Low-GI diets reduced A1C by 0.43% after an average duration of 10 weeks. The average GI was 83 for high-GI diets and 65 for low-GI diets. The researchers concluded that selecting low-GI foods has a small but clinically relevant effect on medium-term glycemic control, similar to that offered by medications that target postprandial blood glucose excursions.¹⁰

Low-GI diets resulted in lower A1C and higher HDL but no significant change in weight, according to Ajala et al.⁵

HIGH-FIBER

A survey of 15 studies examined the relationship between fiber intake and glycemic control. Interventions ranged from an additional 4 to 40 g of fiber per day, with a mean increase of 18.3 g/d. Additional fiber lowered A1C by 0.26% in 3 to 12 weeks, compared to placebo. The overall mean fasting blood glucose reduction was 15.32 mg/dL. No study lasted more than 12 weeks, but it is inferred that a longer study could result in a greater A1C reduction. Current dietary guidelines for patients with diabetes exceed the amount of fiber included in most of these studies.¹¹

VEGAN

Ajala et al observed that patients on a vegan diet had lower total cholesterol, LDL, and A1C levels, compared to those on a low-fat diet. At 18 months, the vegetarian diet demonstrated improvement in glucose control and lipids, but not weight loss.⁵

In one RCT, a low-fat vegan diet was shown to improve glycemic control and lipid levels more than a conventional diabetes diet did. A1C decreased by 1.23% over 22 weeks, compared to 0.38% in the conventional diet group. Body weight decreased by 6.5 kg and LDL cholesterol decreased by 21.2% with the vegan diet, compared with a weight loss of 3.1 kg and a 10.7% LDL reduction in the conventional diet group.¹²

Patients on the vegan diet derived energy primarily from carbohydrates (75%), protein (15%), and fat (10%) by eating fruits, vegetables, grains, and legumes. Portion size and caloric and carbohydrate intake were not restricted. The conventional diet involved a caloric intake mainly from a combination of carbohydrates and monounsaturated fats (60% to 70%), protein (15% to 20%), and saturated fat (< 7%). The diet was individualized based on caloric needs and participants’ lipid levels. All participants were given calorie intake deficits of 500 to 1000 kcal/d.¹³ Participants rated both diets as satisfactory, with no significant differences between groups. The researchers concluded that a low-fat vegan diet has acceptability similar to that of a more conventional diabetes diet.¹²

CONCLUSION

Diabetes management strategies may incorporate a variety of dietary plans. While study populations are small and study durations relatively short, the aforementioned diets show improvement in biochemical markers such as fasting glucose, A1C, and lipid levels. The Mediterranean diet is believed to be sustainable over the long term, given the duration of time that people in the region have survived on it. Low-carbohydrate diets, including the Atkins and Paleolithic diets, are very effective at lowering A1C and triglycerides. Vegetarian/vegan diets may be more acceptable to patients than previously thought.

The long-term impact of any eating pattern will likely relate to adherence; adherence is more likely when patients find a diet to be acceptable, palatable, and easy to prepare. Diet selection should incorporate patient preferences and lifestyle choices, and when possible, should involve an RDN with expertise in diabetes.