A meta-analysis by Chinese investigators found that low-carb diets improve cardiovascular risk factors. Specifically: body weight (lowered), triglycerides (lowered), HDL-cholesterol (raised), blood pressure (lowered systolic and diastolic, but less than 2 points).
Additionally, they found increases in total cholesterol and HDL-cholesterol. Some consider those to be going in the wrong direction, increasing cardiovascular risk. The study authors, however, considered these increases “slight,” implying lack of real-world significance.
I’ll not fisk the entire research paper. Have a go at it yourself by clicking the link to full-text below.
The researchers included 12 randomized controlled trials in their analysis. They defined low-carb diets as having less than 40% of calories derived from carbohydrates. If you’re eating 2200 calories a day, 39% of calories from carb would be 215 g of carbs/day. That’s a lot of carb, and wouldn’t be much lower than average. I scanned the report pretty quickly and didn’t run across an overall average for carb grams or calories in the low-carb diets. The “control diets” had 45–55% of calories from carbohydrate.
Here’s the abstract:
Low-carbohydrate diets are associated with cardiovascular risk factors; however, the results of different studies are inconsistent.
The aim of this meta-analysis was to assess the relationship between low-carbohydrate diets and cardiovascular risk factors.
Four electronic databases (PubMed, Embase, Medline, and the Cochrane Library) were searched from their inception to November 2018. We collected data from 12 randomized trials on low-carbohydrate diets including total cholesterol, high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), triglycerides, and blood pressure levels, as well as weight as the endpoints. The average difference (MD) was used as the index to measure the effect of a low-carbohydrate diet on cardiovascular risk factors with a fixed-effects model or random-effects model. The analysis was further stratified by factors that might affect the results of the intervention.
From 1292 studies identified in the initial search results, 12 randomized studies were included in the final analysis, which showed that a low-carbohydrate diet was associated with a decrease in triglyceride levels of -0.15mmol/l (95% confidence interval -0.23 to -0.07). Low-carbohydrate diet interventions lasting less than 6 months were associated with a decrease of -0.23mmol/l (95% confidence interval -0.32 to -0.15), while those lasting 12–23 months were associated with a decrease of -0.17mmol/l (95% confidence interval -0.32 to -0.01). The change in the body weight in the observation groups was -1.58kg (95% confidence interval -1.58 to -0.75); with for less than 6 months of intervention, this change was -1.14 kg (95% confidence interval -1.65 to -0.63),and with for 6–11 months of intervention, this change was -1.73kg (95% confidence interval -2.7 to -0.76). The change in the systolic blood pressure of the observation group was -1.41mmHg (95% confidence interval—2.26 to -0.56); the change in diastolic blood pressure was -1.71mmHg (95% confidence interval—2.36 to -1.06); the change in plasma HDL-C levels was 0.1mmHg (95% confidence interval 0.08 to 0.12); and the change in serum total cholesterol was 0.13mmol/l (95% confidence interval 0.08 to 0.19). The plasma LDL-C level increased by 0.11mmol/l (95% confidence interval 0.02 to 0.19), and the fasting blood glucose level changed 0.03mmol/l (95% confidence interval -0.05 to 0.12),which was not significant.
This meta-analysis confirms that low-carbohydrate diets have a beneficial effect on cardiovascular risk factors but that the long-term effects on cardiovascular risk factors require further research.
Steve Parker, M.D.
PS: The Paleobetic Diet provides roughly 60 grams/day of digestible carbohydrate.