by Charles O. Frazier, MD, FAAFP
January 2026

For weight loss, I generally recommend a low-carbohydrate eating pattern. Evidence from meta-analyses supports several potential advantages, including greater weight loss (often modestly more compared to low-fat diets and dependent on follow-up duration), higher energy expenditure, and improvements in some cardiometabolic risk factors (Lei 2022; Feng 2025).

What are carbohydrates?

The diet is made up of three major macronutrients: protein, fat, and carbohydrate. Carbohydrates include sugars, starches (chains of sugars), and fiber. Low-carbohydrate diets primarily target reductions in sugars and starches, since starch is broken down into sugar during digestion.

Safety first

Before starting a low-carbohydrate diet, discuss it with your clinician, especially if you have high blood pressure, heart disease, or kidney disease. Lower-carb plans are typically higher in fat and/or protein, and the type of fat and the amount of protein may matter in these conditions.

What the evidence shows

Earlier meta-analyses found that low-carbohydrate diets produced greater weight loss than low-fat diets, with variable effects on cardiovascular risk markers depending on the diet composition and degree of carbohydrate restriction (Sackner-Bernstein 2015; Mansoor 2016). More recent reviews also report improvements in weight and several cardiometabolic measures, while emphasizing that results vary by study design and adherence (Lei 2022; Feng 2025).

Why low-carbohydrate diets may work

• Lower insulin levels, which may promote fat breakdown (Hernandez 2010; de Luis 2015; Boden 2005)
• Higher energy expenditure reported in multiple studies (Ebbeling 2012; Ebbeling 2018; Ebbeling 2020)
• Higher protein effects: protein has a higher thermic effect (diet-induced thermogenesis) and helps preserve lean mass and resting energy expenditure (Moon 2020)
• Reduced appetite, which has been reported in low-carbohydrate and ketogenic patterns (Kirkpatrick 2019; Gibson 2015; Deemer 2020; Roekenes 2021)
• Gut hormone effects: higher-protein patterns may increase satiety hormones and reduce ghrelin (Moon 2020)

How low is "low carb"?

One practical way to define carbohydrate intake is by percent of total calories. The National Academies cite an acceptable macronutrient distribution range for carbohydrates of about 45% to 65% in adults (USDA 2021; NAS 2006). A common classification is:

• Moderate carbohydrate: 26% to 44% of calories
• Low carbohydrate: 10% to 25% of calories
• Very low carbohydrate: under 10% of calories (Kirkpatrick 2019)

For an 1,800-calorie pattern, this corresponds to roughly 115 to 200 g/day (moderate), 45 to 110 g/day (low), and under 45 g/day (very low).

Ketosis and why I do not typically recommend it

Very-low-carbohydrate diets may induce ketosis, a metabolic state where the body uses ketone bodies (from fat breakdown) as a major fuel source when carbohydrate availability is low. The carbohydrate threshold for ketosis varies by individual and depends on the fat-to-protein ratio (Kirkpatrick 2019).

While ketogenic diets can produce substantial initial weight loss, I generally prefer a plan that is low in carbohydrates but not low enough to trigger ketosis. Reasons include:

• Startup side effects are common (often called the "keto flu"): aches, headache, fatigue, nausea, dizziness, brain fog, gastrointestinal symptoms, and palpitations, typically improving within weeks (Bostock 2020; Skartun 2025).
• Lipid effects: very-low-carbohydrate patterns can raise LDL cholesterol, even when HDL increases; some recent evidence suggests LDL increases may be more pronounced in leaner individuals (Fechner 2020; Wang 2024; Soto-Mota 2024).
• Inflammation signals: some studies report increases in markers such as C-reactive protein, although findings vary and may be influenced by diet composition (Rosenbaum 2019; Rondanelli 2022).
• Long-term outcomes and food quality: one meta-analysis suggested higher mortality risk when lower-carbohydrate diets emphasized animal-based fats (Seidelmann 2018), and strict ketosis can crowd out many nutrient-rich foods such as fruit, whole grains, and legumes.

 

References
Lei L, Huang J, Zhang L, Hong Y, Hui S, Yang J. Effects of low-carbohydrate diets versus low-fat diets on metabolic risk factors in overweight and obese adults: A meta-analysis of randomized controlled trials. Front Nutr. 2022 Aug 9;9:935234.

Feng S, Liu R, Thompson C, Colwell B, Chung S, Barry A, Wang H. Effects of carbohydrate-restricted diets and macronutrient replacements on cardiovascular health and body composition in adults: a meta-analysis of randomized trials. Am J Clin Nutr. 2025 Nov;122(5):1461-1478.

Sackner-Bernstein J, Kanter D, Kaul S. (2015) Dietary Intervention for Overweight and Obese Adults: Comparison of Low-Carbohydrate and Low-Fat Diets. A Meta-Analysis. PLoS ONE 10(10):e30139817.

Mansoor N, Vinknes KJ, Veierod MB, Retterstol K. (2016) Effects of low-carbohydrate diets v. low-fat diets on body weight and cardiovascular risk factors: a meta-analysis of randomized controlled trials. British Journal of Nutrition 115:466-479.

Ebbeling CB, Swain JF, Feldman HA, Wong WW, Hachey DL, Garcia-Lago E, Ludwig DS. Effects of dietary composition on energy expenditure during weight-loss maintenance. JAMA. 2012 Jun 27;307(24):2627-34.

Ebbeling CB, Feldman HA, Klein GL, Wong JMW, Bielak L, Steltz SK, Luoto PK, Wolfe RR, Wong WW, Ludwig DS. Effects of a low carbohydrate diet on energy expenditure during weight loss maintenance: randomized trial. BMJ. 2018 Nov 14;363:k4583. (Erratum in: BMJ. 2020 Nov 3;371:m4264.)

Ebbeling CB, Bielak L, Lakin PR, Klein GL, Wong JMW, Luoto PK, Wong WW, Ludwig DS. Energy Requirement Is Higher During Weight-Loss Maintenance in Adults Consuming a Low- Compared with High-Carbohydrate Diet. J Nutr. 2020 Aug 1;150(8):2009-2015.

Moon J, Koh G. Clinical Evidence and Mechanisms of High-Protein Diet-Induced Weight Loss. J Obes Metab Syndr. 2020 Sep 30;29(3):166-173.

U.S. Department of Agriculture and U.S. Department of Health and Human Services. Dietary Guidelines for Americans, 2020-2025. 9th Edition. December 2020. Available at: https://www.dietaryguidelines.gov. Accessed 1/6/2026.

National Academies of Science. Dietary Reference Intakes. The Essential Guide to Nutrient Requirements (2006). Available at: https://www.nationalacademies.org/read/11537/chapter/1 . Accessed 1/6/2026.

Kirkpatrick CF, Bolick JP, Kris-Etherton PM, Sikand G, Aspry KE, Soffer DE, Willard KE, Maki KC. Review of current evidence and clinical recommendations on the effects of low-carbohydrate and very-low-carbohydrate (including ketogenic) diets for the management of body weight and other cardiometabolic risk factors: A scientific statement from the National Lipid Association Nutrition and Lifestyle Task Force. J Clin Lipidol. 2019 Sep-Oct;13(5):689-711.e1.

Bostock ECS, Kirkby KC, Taylor BV, Hawrelak JA. Consumer Reports of "Keto Flu" Associated With the Ketogenic Diet. Front Nutr. 2020 Mar 13;7:20.

Skartun O, Smith CR, Laupsa-Borge J, Dankel SN. Symptoms during initiation of a ketogenic diet: a scoping review of occurrence rates, mechanisms and relief strategies. Front Nutr. 2025 Mar 26;12:1538266.

Fechner E, Smeets ETHC, Schrauwen P, Mensink RP. The Effects of Different Degrees of Carbohydrate Restriction and Carbohydrate Replacement on Cardiometabolic Risk Markers in Humans-A Systematic Review and Meta-Analysis. Nutrients. 2020 Apr 2;12(4):991.

Wang Z, Chen T, Wu S, Dong X, Zhang M, Ma G. Impact of the ketogenic diet as a dietary approach on cardiovascular disease risk factors: a meta-analysis of randomized clinical trials. Am J Clin Nutr. 2024 Aug;120(2):294-309.

Soto-Mota A, Flores-Jurado Y, Norwitz NG, Feldman D, Pereira MA, Danaei G, Ludwig DS. Increased low-density lipoprotein cholesterol on a low-carbohydrate diet in adults with normal but not high body weight: A meta-analysis. Am J Clin Nutr. 2024 Mar;119(3):740-747.

Rosenbaum M, Hall KD, Guo J, Ravussin E, Mayer LS, Reitman ML, Smith SR, Walsh BT, Leibel RL. Glucose and Lipid Homeostasis and Inflammation in Humans Following an Isocaloric Ketogenic Diet. Obesity (Silver Spring). 2019 Jun;27(6):971-981.

Rondanelli M, Perna S, Ilyas Z, Peroni G, Bazire P, Sajuox I, Maugeri R, Nichetti M, Gasparri C. Effect of very low-calorie ketogenic diet in combination with omega-3 on inflammation, satiety hormones, body composition, and metabolic markers. A pilot study in class I obese subjects. Endocrine. 2022 Jan;75(1):129-136.

Seidelmann SB, Claggett B, Cheng S, Henglin M, Shah A, Steffen LM, Folsom AR, Rimm EB, Willett WC, Solomon SD. Dietary carbohydrate intake and mortality: a prospective cohort study and meta-analysis. Lancet Public Health. 2018 Sep;3(9):e419-e428.