Low-carb and keto eating
Quick answer. Low-carb eating cuts back on bread, sugar and starch. Keto cuts back far enough that the body starts making ketones for fuel. In trials, people lose about as much weight on low-carb diets as on balanced diets over one to two years. No randomized trial has tested keto in people taking GLP-1 medicines, and people with diabetes need medical supervision before combining them.
What it is
There is no single definition. The Cochrane review used these bands: low-carbohydrate means more than 50 grams to 150 grams a day or under 45% of calories, and very low means 50 grams a day or less, or under 10% of calories. A ketogenic diet sits in that very low band. At that level the body shifts toward burning fat and producing .
What trials show
The largest summary is a 2022 Cochrane review of 61 randomized trials with 6,925 adults. It compared low-carbohydrate weight-loss diets with balanced-carbohydrate diets, which it defined as 45% to 65% of calories from carbohydrate. In people without diabetes, the low-carb groups lost about 1.1 kg more at 3 to 8.5 months and about 0.9 kg more at one to two years. The authors call that probably little to no difference. In people with type 2 diabetes the gap was 1.3 kg at 3 to 6 months and 0.3 kg at one to two years, and the longer figure could easily be zero.
The review also found the evidence on side effects too thin to draw conclusions. Most of the trials had a high risk of bias, mainly because many people dropped out.
One well-run example is DIETFITS. It randomized 609 adults without diabetes to a healthy low-fat or a healthy low-carb diet for 12 months. The low-fat group lost 5.3 kg and the low-carb group lost 6.0 kg, a difference of 0.7 kg that was not statistically significant. Neither genetic patterns nor insulin response predicted who did better on which diet. The low-carb group averaged about 30% of calories from carbohydrate, so it was low-carb but not keto.
The Atlas did not find a randomized trial of keto in people taking GLP-1 medicines. The big medicine trials, such as STEP and SURMOUNT, paired the drug with calorie-reduced eating and counseling rather than keto.
What experts say about keto with a GLP-1 medicine
The 2025 advisory from four U.S. nutrition and obesity societies says a very-low-carbohydrate diet can be a practical approach for some people, while others find it hard to keep up. If you choose it, it advises building the diet around minimally processed foods, plenty of high-fiber vegetables and nutrient-dense choices.
It raises one clear safety flag. For people with type 2 diabetes, combining a ketogenic diet with a GLP-1 medicine could raise the risk of low blood sugar and diabetic ketoacidosis, a dangerous buildup of acids in the blood. Insulin and sulfonylurea doses may need to be lowered or stopped, and that should happen under careful monitoring by the clinician managing your diabetes.
The advisory also reminds readers that eating much less overall makes nutrient gaps more likely, so what you eat matters more. The beginner guide covers protein, fluids and constipation in chapter 8.
What people report
Large online communities of people on GLP-1 medicines talk about low-carb and keto eating a lot. The themes people commonly describe are a quieter appetite on top of what the medicine already does, trouble getting enough fiber, constipation, and a rough first week of headache and tiredness that people call the keto flu. Many also describe adding salt, potassium or magnesium, or using electrolyte drinks.
None of this was measured. People who do well are more likely to post, people who quit rarely report back, and nobody confirms the details. It is here because enough people say these methods help that you will hear about them, not because it shows they work.
On electrolytes specifically, the Atlas found no trial testing supplements for people eating low-carb on these medicines. If you are considering potassium or other supplements, ask a clinician first, especially with kidney disease or blood pressure medicine.
Who needs to be careful
- Anyone with type 2 diabetes, especially if they take insulin or a sulfonylurea.
- Anyone with kidney disease, gallbladder problems or a history of disordered eating, who should talk to a clinician first.
- Anyone whose appetite is already very low, because a restrictive diet on top can make it hard to eat enough protein and vitamins.
Questions to bring to a clinician or dietitian
- Would a low-carb approach make sense for my health history?
- Do my diabetes or blood pressure medicines need to change if I eat this way?
- How do I get enough fiber and protein while eating little?
- Should we check my kidney function or vitamin levels?
What is still unknown
- Whether keto adds anything to a GLP-1 medicine is untested.
- Long-term results beyond one to two years are limited.
- Safety data on side effects are thin in the main review.
- Whether electrolyte supplements help or harm on these medicines is untested.
Related pages
Sources
- Low-carbohydrate versus balanced-carbohydrate diets for reducing weight and cardiovascular risk Naude CE, et al. Cochrane Database Syst Rev. 2022;1(1):CD013334. PMID 35088407. Funding: Not stated in the abstract. Journal article
- Effect of low-fat vs low-carbohydrate diet on 12-month weight loss in overweight adults (DIETFITS) Gardner CD, et al. JAMA. 2018;319(7):667-679. PMID 29466592. Funding: Not stated in the abstract. Journal article
- Nutritional priorities to support GLP-1 therapy for obesity: a joint advisory from the American College of Lifestyle Medicine, the American Society for Nutrition, the Obesity Medicine Association, and the Obesity Society Mozaffarian D, et al. Obes Pillars. 2025;15:100181. PMID 40673264. Funding: Professional societies; several authors report industry relationships. Journal article