The most common worry about keto, and a fair one, is the heart. A diet built on fat sounds like it ought to be bad for cholesterol and blood vessels, and plenty of people are told exactly that. So it is worth looking at what the trial evidence actually shows rather than what either side asserts. A 2022 meta-analysis is a good place to start, because it pooled a lot of trials and looked specifically at heart risk factors.
What was studied
Luo and colleagues, in Frontiers in Nutrition, combined 21 randomised controlled trials covering 1,074 people who were overweight or obese, some with type 2 diabetes and some without. They compared low-carbohydrate ketogenic diets against non-ketogenic diets and measured the markers doctors use to judge heart risk: blood fats, blood pressure, blood sugar, weight and the rest. Pooling trials like this gives a more reliable read than any single study.
What improved
Several markers moved in a healthy direction. Triglycerides, a blood fat strongly tied to heart risk, fell. HDL, the so-called good cholesterol, rose. Body weight, BMI and waist circumference all came down, and in the participants with type 2 diabetes, blood sugar and HbA1c improved markedly too. Taken together, that is a cluster of changes most people would be pleased to see on a blood test.
What did not change
This is the part that keeps the picture honest. The analysis found no significant change in total cholesterol or in LDL, the so-called bad cholesterol, and no significant change in blood pressure, on average across the trials. So the diet did not, on the whole, lower LDL, and it did not raise it as a group either. That average hides real individual variation, because a minority of people do see their LDL climb noticeably on keto, which is precisely why it is worth measuring rather than assuming. Kidney markers like creatinine were also unchanged, which is reassuring as far as it goes.
The limitation that matters most
The biggest caveat is built into the kind of study this is. It measured risk factors, the markers that predict heart disease, not heart attacks, strokes or deaths themselves. Improving triglycerides and HDL is genuinely good, but it is a proxy for heart health, not a direct measurement of it, and the authors said as much, calling for longer studies that track actual heart events. There was also variety between the trials in which comparison diets were used and how long they ran, which adds some fuzziness. So this tells us keto improves several heart risk markers; it does not, on its own, prove it prevents heart disease.
What it means in practice
The sensible reading is neither the scare story nor the all-clear. On average, a ketogenic diet improved more heart risk markers than it worsened, particularly triglycerides, HDL, weight and blood sugar, while leaving cholesterol and blood pressure broadly unchanged at the group level. The individual exceptions, especially the people whose LDL rises, are real and are the reason this is something to monitor rather than ignore.
In practice that means if you follow keto, getting a blood panel done before and a few months in is simply good sense, so you are working from your own numbers rather than a population average. If your LDL jumps a lot, that is worth a conversation with your doctor about whether the way you are doing keto, particularly the type of fat you lean on, needs adjusting. The quality of the fats matters, and our beginners guide touches on building the diet around whole foods rather than a free pass for any fat going.
The bottom line
A 2022 meta-analysis of 21 trials found that ketogenic diets improved triglycerides, HDL, weight and blood sugar, with no significant average change in LDL, total cholesterol or blood pressure. The big asterisk is that these are risk markers, not heart-disease outcomes, and that some individuals respond differently, which is the case for monitoring your own results rather than trusting either the hype or the horror stories.
This is general information about the ketogenic diet, not medical advice. If you have heart disease, high cholesterol, or other cardiovascular risk factors, speak to your doctor before starting keto and have your blood markers checked so any changes are caught early.
Source: Luo W, Zhang J, Xu D, et al. Low carbohydrate ketogenic diets reduce cardiovascular risk factor levels in obese or overweight patients with T2DM: A meta-analysis of randomized controlled trials. Frontiers in Nutrition. 2022;9:1092031. Read it here.