The Ketogenic Diet (Keto)
The ketogenic diet (keto) is a high-fat, very-low-carbohydrate diet designed to shift the body's primary fuel source from glucose to fat. When carbohydrate intake drops below a critical threshold (typically under 50 grams per day), the liver begins converting fatty acids into ketone bodies, an alternative energy source for the brain and other organs. This state, known as ketosis, is the foundation of ketogenic eating. Advocates argue that because ketones are a more stable fuel than glucose, this metabolic shift leads to better energy regulation, appetite control, and fat burning. The theory is especially appealing to those with insulin resistance, where carbohydrate metabolism is impaired. The carnivore diet, a more extreme subtype of keto that eliminates all plant foods, adheres to the same metabolic principles: achieving ketosis through complete carbohydrate exclusion and protein and fat-rich animal foods.
Effectiveness for Weight Loss
Meta-analyses and clinical trials consistently show that ketogenic diets can lead to substantial short-term weight loss, often outperforming low-fat diets over periods of up to 12 months. Some studies report higher average weight losses than low-fat comparators in the first 6 months. However, the advantage tends to diminish over time. By one year, differences in weight loss between ketogenic and other diets are often no longer statistically significant. Ketosis is associated with reduced hunger, improved appetite control, and increased satiety, potentially making it easier to maintain a calorie deficit. Metabolically, keto improves several markers in individuals with type 2 diabetes and metabolic syndrome. It has been shown to enhance glycemic control, reduce triglycerides, increase HDL cholesterol, and lower fasting insulin levels. A growing body of research also suggests that keto may reduce visceral adiposity and modulate appetite-regulating hormones like leptin and ghrelin.
Carnivore Diet
A subset of keto gaining attention is the carnivore diet: a plant-free regimen consisting entirely of animal foods such as meat, eggs, and sometimes dairy. While even more restrictive, it shares metabolic mechanisms with keto: carbohydrate elimination, reduced insulin, and ketosis. The largest observational study of carnivore diet adherents (n=2029) found that the majority self-reported improved body weight, energy, mood, and symptoms related to autoimmune or gastrointestinal conditions. Participants also reported discontinuing medications and experiencing minimal adverse effects. However, these findings are based on self-reporting and lack control groups, limiting their scientific weight. Mechanistically, carnivore diets may function similarly to keto but with even higher protein and saturated fat intake and zero fiber or phytonutrients. While this works for some, it raises nutritional concerns about micronutrient adequacy, gut microbiome diversity, and long-term cardiovascular health.
Limitations and Considerations
Despite its benefits, keto is not a universal solution. Long-term adherence remains a challenge due to dietary restrictiveness, potential side effects (e.g., constipation, fatigue, nutrient deficiencies), and the exclusion of many health-promoting plant-based foods. Moreover, while most of the evidence supports short- to medium-term benefits, there is little high-quality data on long-term cardiovascular outcomes, mortality, or quality-of-life metrics. In fact, a 2023 umbrella review rated LDL-C (bad cholesterol) rise as one of the few ketogenic outcomes supported by high-certainty evidence, highlighting a potential cardiovascular trade-off that should be considered, particularly in individuals at elevated risk.
Bottom Line
The ketogenic diet is effective for short-term weight loss and offers meaningful metabolic benefits, especially for individuals with insulin resistance or type 2 diabetes. Individual responses vary, and long-term sustainability is a known challenge. The carnivore diet may be viewed as a valid ketogenic strategy, with some promising anecdotes but little controlled evidence.