The idea that diet affects acne went in and out of fashion for decades, often dismissed entirely. The picture has shifted, and there is now genuine trial evidence that the kind of carbohydrate you eat influences breakouts. For anyone eating low-carb who has noticed their skin improve, this is the research behind it.
The landmark study
The most-cited evidence is a randomised controlled trial by Smith and colleagues, published in the American Journal of Clinical Nutrition in 2007. They put young men with acne on either a low-glycaemic-load diet, lower in sugar and refined carbohydrate, or a normal diet, for twelve weeks. The low-glycaemic group saw their acne lesion counts fall substantially more than the control group, roughly twice the improvement, and they also lost a little weight and, tellingly, improved their insulin sensitivity. That last detail is the clue to why it works.
Why blood sugar and insulin matter for skin
The link runs through hormones. Carbohydrate that spikes your blood sugar quickly, the high-glycaemic stuff like sugar, white bread and sweet drinks, drives up insulin and a related growth factor called IGF-1. Both of these stimulate the skin to produce more oil, encourage the skin cells that clog pores to overgrow, and feed the inflammation that turns a blocked pore into an angry spot. Eat in a way that keeps blood sugar and insulin steadier, and you turn down that whole hormonal cascade. A low-glycaemic or low-carb diet does exactly that, which is the proposed reason the skin calms down.
Where keto fits
Here is the honest framing. The strong trial evidence is for low-glycaemic diets rather than strict keto specifically, and a ketogenic diet is essentially the far end of that same spectrum, very low in the fast carbohydrates that drive the insulin response. So it is reasonable to expect keto to help acne through the same mechanism, and many people report that it does, but the direct, high-quality trials on keto for skin are still limited. A 2024 review looking at ketogenic and low-glycaemic diets for inflammatory skin conditions reached much the same conclusion: promising, mechanistically sensible, but in need of more rigorous keto-specific trials. So the confidence comes from the low-glycaemic evidence and the shared biology, not from a pile of keto acne trials.
What it means in practice
If you have acne and are eating low-carb, there is a fair chance you will see some improvement in your skin, and the research gives that hope a real basis rather than wishful thinking. Cutting the high-glycaemic offenders, sugary drinks, sweets and refined starch, is the part most clearly supported, and keto does that by default. Dairy is worth watching too, as some studies link it to acne in certain people, so notice your own response. None of this makes diet a cure or a substitute for proper skin treatment; acne has several causes, and stubborn or scarring acne deserves a dermatologist. Think of diet as one lever among several, one that happens to have decent evidence behind it.
The bottom line
A randomised trial found that a low-glycaemic-load diet roughly doubled the improvement in acne over twelve weeks compared with a normal diet, alongside better insulin sensitivity, and the biology, less insulin and IGF-1 driving oil and inflammation, explains why. Keto sits at the strict end of that same low-glycaemic spectrum, so it is a reasonable bet for clearer skin even though keto-specific trials are still thin. Worth trying, worth watching your own results, and not a reason to skip the dermatologist if your skin needs one.
This is general information about the ketogenic diet, not medical advice. Acne can need medical treatment; see a doctor or dermatologist for persistent or severe acne. If you are pregnant, on medication, or managing a health condition, speak to a professional before changing your diet.
Source: Smith RN, et al. A low-glycemic-load diet improves symptoms in acne vulgaris patients: a randomized controlled trial. American Journal of Clinical Nutrition. 2007;86(1):107-115. Read it here. See also the 2024 review on diets and inflammatory skin conditions here.