In the study that compared the "low-carb" diet to a traditionally recommended low-fat diet, the one designed to flatten out resulting insulin and glucose curves also allowed them to take far fewer oral diabetes medications and apparently cut both systolic and diastolic pressures. The low-fat diet had no apparent effect on diastolic function or med use or on blood pressures.
On the other hand, the two diets led to about the same declines in weight and waist circumference and lipoprotein-cholesterol levels, reported Prof Helene von Bibra (Technical University Munich, Germany) here at the Prediabetes and the Metabolic Syndrome 2013 Congress.
Many patients with insulin resistance, diabetes, or both have subclinical diastolic dysfunction, with severe prognostic implications if it becomes symptomatic, von Bibra reminded heartwire. About 65% of the 32 patients in the study had abnormal diastolic function as defined echocardiographically by low early diastolic myocardial velocity. That measure in most cases nearly normalized after the low-carb diet, but not after the low-fat diet, she said.
Of 32 overweight or obese diabetic patients (mean body-mass index, 34) without cardiac disease who were engaged in a "rehabilitation program in order to lose weight" that included two hours of supervised aerobic exercise per day, half followed a low-glycemic diet (25% carbohydrate, 45% fat, 30% protein) and the other half a low-fat diet (55% carbohydrate, 25% fat, and 20% protein) for three weeks. The diets provided the same amount of calories. Those on the low-fat diet then switched to the low-glycemic diet for an additional two weeks. Cardiac function by echo and metabolic parameters were assessed daily before and after a 400-kcal breakfast.
From baseline to three weeks, patients on the low-carb diet reduced their use of conventional oral antidiabetic medication by 86%. Those on the low-fat diet reduced them by only 6% by the end of three weeks, but intake went down another 57% by the end of their two-week low-glycemic diet phase. "And still they had improvements in glucose," von Bibra said. Medications other than oral ones for diabetes, such as antihypertensive drugs, were not changed in anyone during the study.
In the low-glycemic-diet group, mean systolic blood pressure declined from 127 mm Hg to 118 mm Hg (p<0.002) after three weeks; diastolic pressures also fell (p<0.04). Neither changed after three weeks for those initially on the low-fat diet, but both "improved in the same direction" as those in the low-glycemic group after two weeks on the low-glycemic diet, von Bibra said.
Laboratory and echo changes in overweight/obese diabetic patients assigned to low-glycemic (n=16) and low-fat (n=16) diets
|Initial assigned diet||Baseline||3 wk||2 wk after crossover to low-carb||p|
|Postprandial glucose (mg/dL)||141||125||—||<0.04|
|Triglycerides (mg/dL)||208||194||138||<0.003 vs 3 wk, <0.004 vs baseline|
|Postprandial glucose (mg/dL)||168||137||127||<0.008 vs baseline|
|E' (cm/s)||10.8||10.7||11.4||<0.02 vs 3 wk|
E'=early diastolic myocardial velocity by tissue-Doppler echocardiography
The gains in diastolic function probably were not independently related to the associated blood-pressure reductions; rather, she proposed, they reflected improvements in myocardial energy utilization on the low-glycemic diet. Insulin resistance can lead to diastolic dysfunction via several pathways, she noted, but the most prominent seems to be myocardial energy deficiency secondary to microvascular dysregulation and mitochondrial imbalances of glucose vs fat oxidation.
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