Very-low-carbohydrate eating is best
Dr. Griauzde was a last-minute replacement speaker for William S. Yancy Jr, MD, of Duke University, Durham, N.C., and presented his slides. She argued that consuming a very low carb diet improves glycemia and that it does not increase but possibly lowers cardiovascular risk.
She began by noting that prior to the discovery of insulin very-low-carb diets had been consumed for over a century to prolong life for people with type 1 diabetes.
“We have long recognized the deleterious role of carbohydrate in type 1 diabetes management, and we have increasingly recognized that role in the management of type 2 diabetes,” said Dr. Griauzde of the University of Michigan in Ann Arbor.
In a small study that compared maintaining a very-low-carb diet for 2 weeks with maintaining a high-carb diet for 2 weeks, total glucose areas under the curve were substantially lower (P < .05) during the low-carb phase, while A1c levels dropped from 7.3% to 6.8% (P = .006).
“We don’t see those outcomes with meds,” Dr. Griauzde noted, adding, “A diet very low in carbohydrates is one of the most potent tools we have to help our patients achieve glycemic control.”
Dr. Griauzde said that the carbohydrate-insulin model provides an explanation for why dietary carbohydrates are particularly obesogenic and metabolically harmful. That model contrasts with the energy balance model, which suggests that all calories are equal.
The rationale of the carbohydrate-insulin model is that dietary carbohydrate – either sugar or starch – raises serum glucose and insulin levels. A carbohydrate-restricted diet therefore reduces the dietary contribution to serum glucose, which then results in lower insulin levels. Insulin is a potent stimulator of lipogenesis (fat storage), and it is a potent inhibitor of lipolysis (the burning of fat). By lowering insulin levels, stored body fat is burned, serum ketone levels increase, and body weight is lowered.
This model suggests that, when insulin levels are chronically high because of excess carbohydrate consumption, circulating fuels are lowered, which leads to an increase in hunger and to overeating. This was demonstrated in a study that compared different levels of isocaloric glycemic index diets in 12 teenage boys with overweight or obesity. The higher-carbohydrate meals led to higher glucose and insulin levels and more food consumption.
In a systematic review of 13 trials of restricted-carbohydrate diets (< 45% carbohydrates) for adults with diabetes, the degree of improvement in A1c level correlated with the degree of carbohydrate restriction over 2-26 weeks (P = .013).
And in a network meta-analysis of 56 trials that compared nine diets among a total of 4,937 participants with type 2 diabetes, one conclusion was that “for reducing A1c, the low-carbohydrate diet was ranked as the best dietary approach (SUCRA: 84%), followed by the Mediterranean diet (80%), and Paleolithic diet (76%), compared with a control diet.”
Regarding the criticism that very-low-carbohydrate diets are high in saturated fat and therefore raise the risk of cardiovascular disease, Dr. Griauzde pointed to another meta-analysis of 21 prospective studies with more than 300,000 participants with 5-25 years of follow-up. In that analysis, the intake of saturated fat was not associated with an increased risk of cardiovascular disease or stroke.
Furthermore, a 12-week randomized controlled trial that involved 40 adults with overweight also suggested that a very-low-carb diet may be superior to a low-fat diet in improving aspects of the metabolic syndrome, including body mass index, lipid levels, and insulin sensitivity. Small LDL particles, which are more atherogenic than larger LDL particles, also decreased despite a threefold increase in saturated fat intake.