First of all, why do conventional diets advocate restricting saturated and total fat? From the standpoint of surrogate markers of cardiovascular risk, cutting saturated and total fat reduces total cholesterol; reduces calculated LDL cholesterol; and may reduce c-reactive protein modestly (an index of inflammation). It also increases blood sugar and HbA1c (reflecting the prior 60 days blood sugars), increases glycation of the proteins of the body leading to cataracts, arthritis, and hypertension.
Problem: Total cholesterol is a combination of HDL cholesterol, an estimate of VLDL cholesterol (triglycerides), and LDL cholesterol. It is a composite of both "good" things (HDL) and "bad" things (LDL and VLDL). Cutting saturated and total fat results in reduced HDL, increased VLDL/triglycerides, and a reduction in calculated LDL. Pretty weak stuff. The last item, i.e., reduction in calculated LDL, is not even a real phenomenon. In fact, the net effect in most genotypes (genetic types) may be negative: increased heart disease risk.
In contrast, what is the effect of reducing carbohydrate without restricting fat? (In the approach I use, we start with elimination of the most destructive of carbohydrates, wheat, followed by reducing exposure to other carbohydrates, especially cornstarch and corn products, sugar, and oats.) If, say, we cut carbohydrate intake into the range of a truly low-carbohydrate diet of 10-15 grams per meal ("net" carbs, or total carbohydrates minus fiber), then we witness a number of metabolic transformations:
- Reduced fasting triglycerides and VLDL
- Reduced postprandial (after-eating) triglycerides, chylomicrons, and chylomicron remnants
- Increased HDL and shift towards large HDL particles (presumably more protective)
- Reduced small LDL particles
- Reduced glycation and oxidation of small LDL particles
- Reduced hemoglobin A1c
- Reduced c-reactive protein and other inflammatory markers
- Reduced blood pressure
Having personally gone down the diabetic path and back by cutting the fat in my diet, now maintaining a HbA1c of 4.8% with fasting glucose 84 mg/d; (without medications), there should be no remaining doubt: Low-carb diets, especially if wheat-free, dramatically reduce the factors leading to heart disease; low-fat diets worsen the factors leading to heart disease.