In 1797 John Rollo (England) successfully treated a patient with a high fat and protein diet after observing that sugar in the urine increases after eating starchy food. At that time it was considered the first
significant approach to the treatment of diabetes. Since that time many diet plans have been recommended including starvation diets and Exchange diets.
Many current popular weight loss diets advocate restricting carbohydrates for weight loss but the benefits and risks of these diets for diabetic patients are unclear.
The purpose of a recent study in the American Journal of Clinical Nutrition (Jan. 30, 2013) surveyed the scientific evidence of different diets to encourage weight loss, improve glycemic control (blood glucose levels) and lipid profiles in people with type 2 diabetes. Chronic elevated levels of blood glucose, low HDL-cholesterol, high LDL-cholesterol and high levels of triglycerides may increase the risk of heart disease and stroke. Diabetes type 2 occurrence increases with age but recently has occurred in greater numbers than ever before in children and adolescents.
Being overweight or obese also increases the risk of developing diabetes type 2 as well as where we store body fat. Abdominal fat increases the risk compared to fat storage in the thighs and hips. Therefore, weight loss plays a major role in the treatment for this disorder.
Many health organizations have made recommendations regarding the best dietary approach to control diabetes type 2. The British Dietetic Association, European Association for the Study of Diabetes and the American Diabetes Association and the Canadian Diabetes Association usually recommend a carbohydrate intake of 50-60% of total energy intake, total fat of less than 30% of energy while restricting saturated fat and trans fat intake.
Most of the diets emphasized controlling total fat, not just saturated or trans fat, but a panel of experts agreed that such an approach appeared to be ineffective. They suggested that low carbohydrate diets were at least as effective as low fat diets for weight loss and that the substitution of fat for carbohydrates was generally beneficial for the risk of heart disease.
Low-carbohydrate diets are frequently taken as synonymous with the Atkins diet which remains controversial due to its presumed higher fat content. In practice, however, many low carbohydrate dieters do not add additional fat. A reduced carbohydrate diet may show a significant percent increase in fat, but there may be no change in the absolute amount consumed. It is also feasible to increase fat intake in the form of healthy fats such as monounsaturated fatty acids, commonly associated with the Mediterranean diet and still avoid saturated and trans fat.
In the meta-analysis, researchers collected data from all studies published up to July 2011 that compared low carbohydrate, vegetarian, vegan, low glycemic, high fiber, Mediterranean and high protein diets with control diets including low-fat, high glycemic, American Diabetes Association diet, European Association for the Study of Diabetes diet, and low-protein diets. Only randomized controlled diet trials with an intervention lasting longer than six months were selected. A total of 20 studies including 3073 people fulfilled the defined criteria. Measured outcomes included glycated hemoglobin (HbA1c which reflects glucose control), difference in weight loss, and changes in HDL-cholesterol (good cholesterol), LDL-cholesterol (bad cholesterol) and triglycerides.
The low-carbohydrate, low GI, Mediterranean and high protein diets all led to a greater improvement of blood glucose control (HbA1c) compared with their respective control diets, with the largest effect seen in the Mediterranean diet even in the absence of weight loss. Low-carbohydrate, low GI, and Mediterranean diets all led to an elevation of HDL-cholesterol. Only the Mediterranean diet led to a significant reduction in triglycerides. The high protein diets had no effect on markers of lipid profiles.
A previous meta-analysis in 2008 had similar results. After analyzing 13 studies, it reported that hemoglobin A1c, fasting glucose, and triglycerides improved with lower carbohydrate-content diets. There were no significant relationships observed for total cholesterol, HDL or LDL cholesterol. (Journal of the American Dietetic Association 2008:108:91-100).
Details of the individual diets may be more important than carbohydrate restriction. For example, elimination of simple sugars and high fructose-containing beverages from the diet may be important factors in better glucose control. Furthermore, even though carbohydrate restriction appears to result in beneficial effects on glucose control and lipids markers, no one knows definitively if carbohydrate restriction results in better outcomes of cardiovascular disease itself.
In light of the current evidence maybe it is time to re-appraise the role of carbohydrate restriction in terms of health and not just weight loss. There is no simple answer as to whether the lower carbohydrate restriction is the dietary treatment of choice for all type 2 diabetics. In all probability it is probably best to tailor the diet to meet the needs of the individual patient based on their blood glucose and lipid parameters.