Fasting trimmed weight and waists but left cholesterol and blood sugar untouched

Metabolic syndrome bundles together the risk factors that push people towards heart disease and diabetes, so anything that reliably improves those numbers matters to a large slice of the population. Intermittent fasting has been promoted as exactly that kind of fix, and earlier evidence suggested it may benefit people with the syndrome. But the results have been described as controversial and indefinite, with studies pointing in different directions. This review set out to establish what fasting actually does to weight, blood pressure, insulin resistance, blood sugar and blood fats in this group by pooling the randomised trials that exist.

The authors searched four major research databases, PubMed, Web of Science, Embase and the Cochrane Library, for randomised controlled trials published up to 31 July 2022. From 4997 records retrieved, six trials met the inclusion criteria and were pooled. The outcomes covered body composition and cardiometabolic risk together: body mass index, fat mass, fat free mass, body weight, waist circumference, blood pressure, insulin resistance measured by the homeostasis model, fasting blood glucose, fasting insulin and lipid profiles. They then ran subgroup and sensitivity analyses to probe how stable the pooled results were.

Compared with non-fasting, intermittent fasting reduced body weight by 2.49 kg on average, waist circumference by 3.06 cm, and body mass index by 1.56 kg/m2. Fat mass fell by 1.35 percentage points, and insulin resistance improved, with the HOMA-IR score dropping by 0.62. Not everything moved in the desired direction: fat free mass also fell slightly, by 0.63 percentage points. A long list of outcomes did not change at all, including systolic and diastolic blood pressure, total cholesterol, triglycerides, LDL and HDL cholesterol, fasting blood glucose and fasting insulin. Sensitivity analysis suggested the pooled results were reliable and robust.

This pooling helps explain why the fasting literature has felt contradictory: the body composition and insulin resistance benefits look consistent, while the blood pressure and lipid improvements often claimed for fasting did not show up here. The subgroup analyses hinted that study duration and sample size explain why trials disagreed about LDL cholesterol. With only six trials included, the evidence base remains thin, and the authors conclude that larger studies are needed to verify both the effectiveness and the safety of intermittent fasting in this population. Whether longer or bigger trials would eventually shift the blood markers is left an open question.

If you have metabolic syndrome or sit close to it, this is a reason to see intermittent fasting as a workable route to a lighter body, a smaller waist and better insulin sensitivity, rather than as a cure-all for every number on a blood panel. It is also a reason to pay attention to what kind of weight is being lost, since fat free mass declined slightly alongside fat. Anyone fasting specifically to improve cholesterol or blood pressure should know those outcomes did not move in these pooled trials. None of this is a prescription; it is a clearer picture of what the trial evidence currently shows.