Vegan vs Keto: Which Diet Is Actually Better?

Vegan and keto diets sit at opposite ends of the dietary spectrum — one centres on plants and carbohydrates, the other on fat and animal products. Both have passionate advocates, both claim health benefits, and both have real science behind them. Here is an honest comparison covering weight loss, long-term health, sustainability, and practicality.

How each diet works

A vegan diet excludes all animal products. In its whole-food form, it is naturally high in fibre, complex carbohydrates, and micronutrients, and low in saturated fat. The primary fuel source is glucose from carbohydrates.

A ketogenic (keto) diet restricts carbohydrates to roughly 20–50g per day — about 5–10% of total calories — and replaces them with fat (60–75%) and moderate protein (15–30%). This forces the body into ketosis, a metabolic state where fat is broken down into ketone bodies for energy.

Standard keto diets rely heavily on meat, fish, eggs, butter, cheese, cream, and oils. A "vegan keto" diet is theoretically possible but extremely restrictive, eliminating both animal products and most carbohydrate-rich plants.

Weight loss

Both diets can produce significant weight loss, but through different mechanisms:

Keto produces rapid initial weight loss — typically 2–5 kg in the first week. However, most of this is water loss: for every gram of glycogen depleted, the body releases 3–4 grams of water. True fat loss occurs as ketosis suppresses appetite through elevated ketone levels and increased satiety from dietary fat. A 2013 meta-analysis in the British Journal of Nutrition found that keto dieters lost an average of 0.9 kg more than low-fat dieters over 12+ months.

Vegan diets produce steady, sustained weight loss primarily through lower caloric density. Whole plant foods contain more fibre and water per calorie, increasing satiety with fewer calories. The BROAD study (2017), a randomised controlled trial in New Zealand, found that participants on a whole-food plant-based diet lost an average of 11.5 kg over 12 months — without calorie counting or portion control.

Cardiovascular health

This is where the diets diverge most sharply. The evidence overwhelmingly favours plant-based eating for heart health.

Vegan diets consistently lower LDL cholesterol (the primary driver of atherosclerosis) by 15–30% within weeks. The EPIC-Oxford study found vegans had a 22% lower risk of coronary heart disease. Multiple clinical trials by Dr. Dean Ornish and Dr. Caldwell Esselstyn have demonstrated that low-fat, whole-food plant-based diets can reverse coronary artery disease.

Keto diets, by contrast, typically raise LDL cholesterol. A 2023 study presented at the American College of Cardiology found that a low-carb, high-fat diet was associated with a two-fold increase in cardiovascular events. The high intake of saturated fat from meat, butter, and cheese is the primary concern. While some proponents argue that keto raises "large, fluffy" LDL (less harmful), the American Heart Association maintains that total LDL reduction remains the most important factor.

We caution against the use of low-carbohydrate, high-fat ketogenic diets because of their potential to raise LDL cholesterol and increase cardiovascular risk.

Cancer risk

The World Health Organization classifies processed meat as a Group 1 carcinogen and red meat as Group 2A (probably carcinogenic). Keto diets, which are typically high in both, may increase colorectal cancer risk. Vegan diets, rich in fibre and phytochemicals, are associated with lower rates of colorectal, breast, and prostate cancers in observational studies.

Additionally, the fibre content of vegan diets feeds beneficial gut bacteria that produce short-chain fatty acids (SCFAs) — compounds with demonstrated anti-inflammatory and anti-cancer properties. Keto diets, which are very low in fibre, may reduce gut microbiome diversity. A 2020 study in Cell Host & Microbe found that ketogenic diets significantly reduced populations of beneficial Bifidobacteria.

Diabetes and blood sugar

Both diets have evidence for improving blood sugar control, but through different mechanisms:

• Keto reduces blood sugar by eliminating most carbohydrates. This is effective in the short term but does not address the underlying insulin resistance — it simply removes the trigger.
• Vegan (WFPB) diets improve insulin sensitivity at the cellular level. A 2019 meta-analysis in JAMA Internal Medicine found a 23% lower risk of type 2 diabetes with greater plant-based diet adherence. The mechanism is likely reduced intramyocellular lipid accumulation (fat inside muscle cells that blocks insulin signalling).

Environmental impact

There is no contest here. Keto diets, with their heavy reliance on animal products, have a dramatically larger environmental footprint.

The 2018 Oxford study by Poore and Nemecek found that even the lowest-impact animal products exceed the environmental cost of plant alternatives. A keto diet — by design heavy in the most resource-intensive foods (beef, butter, cheese) — has roughly 3x the carbon footprint of a vegan diet. See Veganism and the Environment for more.

Sustainability and long-term adherence

Keto has notoriously poor long-term adherence. The restrictive nature of eliminating nearly all carbohydrates — including fruits, most vegetables, legumes, and whole grains — makes it difficult to maintain. Common side effects include the "keto flu" (headaches, fatigue, irritability during adaptation), constipation from low fibre intake, and bad breath from acetone production.

Vegan diets have better long-term adherence rates in clinical trials, particularly when the focus is on whole foods rather than restriction. The social challenges (dining out, family meals) are real but manageable, and the growing availability of plant-based options continues to make it easier.

If weight loss is your primary goal, see our detailed guide on Vegan Weight Loss: Does It Actually Work?. For the full health picture, read The Health Benefits of a Vegan Diet.