While any diet which induces weight loss creates a negative energy balance (i.e. caloric deficit), the rationale for either high-carbohydrate (high-carb) or low-carbohydrate (low-carb) diets remains in discussion. While any low-carb or high-carb approach results in a decrease or increase in overall daily carbohydrate intake respectively, there is no clear-cut agreement on what defines a low-carbohydrate (low-carb) or high-carbohydrate (high-carb) diet; however above 45% of daily energy intake is generally considered high, and below 26% is low (1).

The rationale behind high-carb (low-fat) diets is that eating fat will make you fat, since fat has a high energy density (with nine calories per gram), opposed to carbohydrates and protein (with four calories per gram) (1). Additionally, despite active lipolysis (fatty breakdown), dietary fat is directly taken up by your adipose (fatty tissue) and deposited as body fat. However, while fat contains more calories than carbohydrates, it is more satiating gram-for-gram (2). And naturally, while fat is directly stored as adipose tissue following a meal, it can also be mobilized and oxidized (or “burned”) for fuel when necessary (3). Net fat balance (fat stored vs fat burned) is what truly determines fat loss or gain. Provided you’re in a caloric deficit, fat being burned will ultimately exceed fat being stored, regardless of how you’re consuming your calories (4).

The rationale behind low-carb (high-fat) diets is that in response to consuming carbohydrate, our body produces insulin, a highly “anabolic” storage hormone which essentially promotes storage of calories as body fat. Therefore, lowering insulin levels by restricting carb intake induces weight (i.e. fat) loss (5). Moreover, as the argument goes, carbs also raise blood glucose (sugar), and are absorbed more rapidly than fat, thus following a high-carb diet will lead to chronically elevated blood sugar and insulin levels, large fluctuations in blood sugar and associated energy levels, and also excessive hunger.

The flaw with this theory however is that protein too raises insulin (6) Also, insulin acts as an appetite suppressant via signals sent to the brain (7). Additionally, though there is an acute increase in blood sugar and insulin levels following carbohydrate consumption, a high-carb diet doesn’t automatically result in chronically elevated blood sugar and insulin. Above all else, insulin isn’t the enemy it’s portrayed to be. While it is a storage hormone, insulin does not only store glucose as fat, but also as glycogen in the muscle tissue and the liver (8). Plus, it only provides the signal for the body to store energy - if there’s no energy input, then none will be stored.

The Ketogenic or “Keto” diet, a popular variation of low carb, essentially results in the production of ketones in the body when glucose (sugar) derived from carbohydrates isn’t available in the bloodstream. Instead we begin to break down stored fats from adipose tissue into molecules called ketone bodies (a process known as ketosis) (9). Once in a state of ketosis, the body will adapt so that the majority of cells have the capacity to “burn” ketone bodies as the predominant fuel source for the body (9). The shift from glucose to fats as an energy source, generally takes two to four days of restricting carb intake to less than 20-50g per day (10). Do not forget that this is a highly individualized process, and some people need a more restricted diet than others to start producing enough ketones.

There is robust evidence showing low carb approaches, specifically ketogenic to be superior to other dietary approaches (namely a more traditional low-fat, high carb diet, or even a Mediterranean diet) in inducing rapid weight loss for the first 6-12 months of dieting (11, 12, 13).

The primary explanation as to why low-carb diets produce an initial faster rate of weight loss compared to other diets is that fats and protein increase satiety therefore reducing hunger which “naturally” results in a reduction in overall calorie intake, producing an energy deficit (14).

What’s more is a low-carb diet can produce a greater thermic effect than a high-carb diet. Recent studies have found there to be a metabolic advantage of around 200 to 300 additional calories burned compared to a calorie equated high-carb diet (5, 15).

As a low carb or keto diet provides very little carbohydrate, it is typically rich in fats and proteins (e.g. meat, eggs, processed meats, sausages, cheeses, fish, nuts) to compensate for the reduction in carbohydrate (16). This inherently means cutting out an entire food group, so is very restricting in food choices, making it much more difficult to adhere to in the long term. This is reflected in the literature where the difference in weight loss seems to even out after one year, once adherence to the diet subsides (17).

To lose weight you must create a caloric deficit; that’s a given. While pretty much any strategy (whether it be low carb or high carb) can be a viable option provided that basic nutritional needs are met, the most important factor is undoubtedly finding the approach that you can stick with. No matter how “good” the plan is conceptually, it’s irrelevant if you can’t adhere to the plan. Despite the hype around certain diets (such as keto), there are no magical formulas! Focus on adopting a diet that fits your lifestyle.


Oh, R. and Uppaluri, K. (2019). Low Carbohydrate Diet. [online] Ncbi.nlm.nih.gov. Available at: https://www.ncbi.nlm.nih.gov/books/NBK537084/.

Warrilow, A., Mellor, D., McKune, A. and Pumpa, K. (2018). “Dietary fat, fibre, satiation, and satiety—a systematic review of acute studies”. European Journal of Clinical Nutrition, 73(3), pp.333-344.

Cohen, P., & Spiegelman, B. M. (2016). Cell biology of fat storage. Molecular Biology of the Cell, 27(16), 2523–2527. doi:10.1091/mbc.e15-10-0749.

Hall, K. D., Bemis, T., Brychta, R., Chen, K. Y., Courville, A., Crayner, E. J., … Yannai, L. (2015). Calorie for Calorie, Dietary Fat Restriction Results in More Body Fat Loss than Carbohydrate Restriction in People with Obesity. Cell Metabolism, 22(3), 427–436. doi:10.1016/j.cmet.2015.07.021 

Ebbeling, C., Feldman, H., Klein, G., Wong, J., Bielak, L., Steltz, S., Luoto, P., Wolfe, R., Wong, W. and Ludwig, D. (2018). “Effects of a low carbohydrate diet on energy expenditure during weight loss maintenance: randomized trial”. BMJ, p.k4583.

Rietman, A., Schwarz, J., Tomé, D., Kok, F. and Mensink, M. (2014). “High dietary protein intake, reducing or eliciting insulin resistance?”. European Journal of Clinical Nutrition, 68(9), pp.973-979.

Pliquett, R., Führer, D., Falk, S., Zysset, S., von Cramon, D. and Stumvoll, M. (2006). “The Effects of Insulin on the Central Nervous System - Focus on Appetite Regulation”. Hormone and Metabolic Research, 38(7), pp.442-446.

Tokarz, V., MacDonald, P. and Klip, A. (2018). “The cell biology of systemic insulin function”. The Journal of Cell Biology, 217(7), pp.2273-2289.

Masood, W. and Uppaluri, K. (2019). Ketogenic Diet. [online] Ncbi.nlm.nih.gov. Available at: https://www.ncbi.nlm.nih.gov/books/NBK499830/.

Campos, M. (2017). Ketogenic diet: Is the ultimate low-carb diet good for you? - Harvard Health Blog. [online] Harvard Health Blog. Available at: https://www.health.harvard.edu/blog/ketogenic-diet-is-the-ultimate-low-carb-diet-good-for-you-2017072712089.

Nordmann, A., Nordmann, A., Briel, M., Keller, U., Yancy, W., Brehm, B. and Bucher, H. (2006). “Effects of Low-Carbohydrate vs Low-Fat Diets on Weight Loss and Cardiovascular Risk Factors”. Archives of Internal Medicine, 166(3), p.285.

Bueno, N., de Melo, I., de Oliveira, S. and da Rocha Ataide, T. (2013). “Very-low-carbohydrate ketogenic diet v. low-fat diet for long-term weight loss: a meta-analysis of randomised controlled trials”. British Journal of Nutrition, 110(7), pp.1178-1187.

Tobias, D., Chen, M., Manson, J., Ludwig, D., Willett, W. and Hu, F. (2015). “Effect of low-fat diet interventions versus other diet interventions on long-term weight change in adults: a systematic review and meta-analysis”. The Lancet Diabetes & Endocrinology, 3(12), pp.968-979.

Krebs, N., Gao, D., Gralla, J., Collins, J. and Johnson, S. (2010). Efficacy and Safety of a High Protein, Low Carbohydrate Diet for Weight Loss in Severely Obese Adolescents. The Journal of Pediatrics, 157(2), pp.252-258.

Ludwig, D. and Ebbeling, C. (2018). “The Carbohydrate-Insulin Model of Obesity”. JAMA Internal Medicine, 178(8), p.1098.

Harvey, C., Schofield, G., Zinn, C., Thornley, S., Crofts, C. and Merien, F. (2019). “Low-carbohydrate diets differing in carbohydrate restriction improve cardiometabolic and anthropometric markers in healthy adults: A randomised clinical trial”. PeerJ, 7, p.e6273.

Gardner, C., Kiazand, A., Alhassan, S., Kim, S., Stafford, R., Balise, R., Kraemer, H. and King, A. (2007). “Comparison of the Atkins, Zone, Ornish, and LEARN Diets for Change in Weight and Related Risk Factors Among Overweight Premenopausal Women”. JAMA, 297(9), p.969.



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