When it comes to weight loss, everyone has an opinion. From low-carb to low-fat, and everything in between, there is no shortage of diets that cater to every preference and taste. But which (if any) of these diets are truly effective at achieving and maintaining long-term, sustainable weight loss?
In today’s post, we’re taking a critical, evidence-based look at the diets of our time to find out which approaches are worth a second glance.
The Ketogenic Diet
A keto (short for ketogenic) diet is a low-carb, high-fat diet that restricts carbohydrate intake to 20-50 g of net carbs (total carbohydrates minus fibre) per day, or 5-10% of total energy (1). While targets for protein and fat vary based on the level of “strictness”, these macronutrients typically provide 20-25% and 65-80% of total energy, respectively.
Weight loss is theorized to occur on a ketogenic diet via several mechanisms: lower body fat stores resulting from less circulating insulin; increased satiety; and a greater production of glucose from protein (which uses a lot of extra energy; 2). Additionally, there is often a reduction in total calorie intake on a keto diet.
When compared to a low-fat diet, a ketogenic diet may result in marginally greater weight loss at the 12-month mark (0.9 kg difference), while improving some risk factors for cardiovascular disease (triglycerides and HDL cholesterol) and potentially worsening others (LDL cholesterol; 3).
As the name implies, low-carb diets (Atkins, South Beach, the Zone) also restrict carbohydrates, but not to the point of inducing ketosis. While “allowable” intake of carbohydrates varies by diet, most advise an intake of < 40% of total calories. A 2014 meta-analysis and systematic review (4) found that compared to no dietary intervention, a low carb diet resulted in a weight loss of 8.73 kg at 6 months and 7.25 kg at 12 months. This rate of weight loss was comparable to a low fat-diet, where total carbohydrate and fat intake equaled 60% and < 20%, respectively (4).
The number of people following a plant-based eating diet jumped by a whopping 600% between 2014 and 2017 (5), thanks in part to popular documentaries and food companies investing in plant-based alternatives like Beyond Meat. In addition, recent guidelines, including both Canada’s Food Guide and the EAT-Lancet report emphasize the importance of plant-based diets to meet global health and environmental initiatives. But can a plant-based diet change an individual’s body weight?
Observational data from the Adventist Health Studies have found that an individual’s body weight increases with the intake of animal foods (i.e. vegans weigh less than vegetarians, who weigh less than pescatarians, who weigh less than omnivores; 6) and data from the EPIC-Oxford trial suggests that vegans have significantly lower rates of age-related weight gain compared to omnivores (7). In a meta-analysis of 15 interventional trials, individuals who followed a plant-based diet (without energy restrictions) for a minimum of 4 weeks lost on average 4.6 kg (8). However, given the short duration of follow-up, it is unknown if these weight changes were sustained long-term.
As discussed in a previous post, intermittent fasting, which typically restricts the eating window to just 6-8 hours per day, is as effective as calorie-restricted diets in achieving weight loss that is maintained at 12-months follow-up (9). In addition, fasting may lead to better insulin control versus calorie-restricted diets, without any additional adverse outcomes (9).
The Bottom Line
So, if weight loss is your goal, which of the above diets should you follow – low carb, keto, vegan, low-fat, or intermittent fasting?
Based on the evidence available to date, it appears that any diet can work, provided you are able to stick with it long-term. In North America, obesity is considered a progressive chronic disease that requires effective, long-lasting interventions to mange. Diets that are too restrictive or have a set end date are unlikely to provide long-lasting results and in fact, can do more harm than good.
Did you know?
Cronometer allows you to customize your keto diet using its keto calculator. There are also many great discussions on how to implement a keto diet on the Cronometer forums (free for anyone to access!).
Keto not for you?
You can also play around with your macronutrient targets in order to align with the diet that best meets your needs.
1. Royall D. Diet Composition: Keto Diets. PEN: Practice-based evidence in Nutrition. 2018 Nov. Access through subscription only: https://www.pennutrition.com/KnowledgePathway.aspx?kpid=25499&trcatid=38&trid=27298
2. Paoli A, Rubini A, Volek JS, Grimaldi KA. Beyond weight loss: a review of the therapeutic uses of very-low-carbohydrate (ketogenic) diets. Eur J Clin Nutr. 2013 Aug;67(8):789-96. Abstract available from: https://www.ncbi.nlm.nih.gov/pubmed/23801097
3. Bueno NB, de Melo IS, de Oliveira SL, da Rocha Ataide T. Very-low-carbohydrate ketogenic diet v. low-fat diet for long-term weight loss: a meta-analysis of randomised controlled trials. Br J Nutr. 2013 Oct;110(7):1178-87. Abstract available from: https://www.ncbi.nlm.nih.gov/pubmed/23651522
4. Johnston BC, Kanters S, Bandayrel K, Wu P, Naji F, Siemieniuk RA, et al. Comparison of weight loss among named diet programs in overweight and obese adults: a meta-analysis. JAMA. 2014 Sep 3;312(9):923-33. Abstract available from: https://www.ncbi.nlm.nih.gov/pubmed/25182101
5. Forgrieve J. The Growing Acceptance of Veganism. Forbes. 2018 Nov. Available from: https://www.forbes.com/sites/janetforgrieve/2018/11/02/picturing-a-kindler-gentler-world-vegan-month/#7412046b2f2b
6. Tonstad S, Stewart K, Oda K, Batech M, Herring RP, Fraser GE. Vegetarian diets and incidence of diabetes in the Adventist Health Study-2. Nutr Metab Cardiovasc Dis. 2013 Apr;23(4):292-9. Abstract available from: https://www.ncbi.nlm.nih.gov/pubmed/21983060
7. Rosell M, Appleby P, Spencer E, Key T. Weight gain over 5 years in 21,966 meat-eating, fish-eating, vegetarian, and vegan men and women in EPIC-Oxford. Int J Obes (Lond). 2006 Sep;30(9):1389-96. Epub 2006 Mar 14. Abstract available from: https://www.ncbi.nlm.nih.gov/pubmed/16534521
8. Barnard ND, Levin SM, Yokoyama Y. A systematic review and meta-analysis of changes in body weight in clinical trials of vegetarian diets. J Acad Nutr Diet. 2015 Jun;115(6):954-69. Abstract available from: https://www.ncbi.nlm.nih.gov/pubmed/25620754
9. Harris L, Hamilton S, Azevedo LB, Olajide J, De Brún C, Waller G, et al. Intermittent fasting interventions for treatment of overweight and obesity in adults: a systematic review and meta-analysis. JBI Database System Rev Implement Rep. 2018 Feb;16(2):507-547. Abstract available from: https://www.ncbi.nlm.nih.gov/pubmed/29419624