Chances are you’ve watched a documentary on Netflix, or read a few magazine articles. It doesn’t take long to discover that there’s a diet war going on in the popular media. On one side, you have the “carbs are evil” hypothesis. People who promote very-low-carb diets (e.g. Keto and Paleo diets) often cite population health studies showing a correlation between carbohydrate intake and metabolic diseases like diabetes, fatty liver disease, obesity and heart disease. In 2013, a meta-analysis of thirteen clinical trials examining the Keto diet versus low-fat diets (LFD) found that people assigned to a Keto diet experienced greater weight loss over a twelve month follow-up period.(1) For people who have medical clearance & support from a health professional to adopt a Keto diet, the very-low-carb approach appears to yield significant weight loss over the short-term.
However, medical support for Keto diets is likely to disappear in the coming decade. That is because, in 2018 new research has linked long-term adoption of Keto diets to an increased risk of death. A recent study published in The Lancet-Public Health journal found that both low-carb and high-carb diets increased the risk of death, with more pronounced negative effects occurring for people who subscribe to very-low-carb diets.(2)
It’s also interesting to note that the Keto diet is ranked 2nd last (#39 out of 40) in the U.S. News Best Diet Rankings. Key concerns are that this diet is known to negatively impact your body’s metabolism when used long-term. Patients who stop the Keto diet – even after several months of dieting – often experience rapid weight regain. Long-term adherence to a Keto diet can also result in muscle loss, fatigue, electrolyte imbalances and GI symptoms. Since very-low-carb diets appear to reduce insulin resistance and fat storage, people sensitive to carbohydrate overload or weight gain might benefit from this approach.
It may seem paradoxical, but a high-carbohydrate vegan diet is an equally popular approach to modern dieting. The “animal fats are evil” hypothesis maintains that people who adhere to a vegan diet – eliminate animal fat and proteins, but increase plant-based foods – have better health outcomes, including lower rates of heart disease and obesity. A two-year clinical trial comparing a vegan diet to a conventional LFD found that weight loss outcomes were superior among those assigned to the vegan group.(3) While this study reported a large effect size, its overall sample size was quite limited (n=62). So, evidence for a vegan diet is compelling, but not as robust as that for a very-low-carb (Keto) approach.
Vegan diets are also quite restrictive, and require professional advice to carry out safely. While a Keto diet is well-studied with disease states (like diabetes), vegan diets have not always shown superiority to other diets in lowering blood sugars. The power of a vegan diet, therefore, appears to reduce heart disease incidence with a high nutrient, blood pressure and cholesterol lowering approach to food consumption. Much like the Keto diet, veganism has some limitations.
You may have noticed that both Keto and Vegan diets are difficult to sustain, and are less commonly recommended by health professionals. While not discussed here, there are more sustainable “vegetarian like” diets (such as the Mediterranean diet) that are a better fit for most people. In some contexts, either a Vegan or Keto diet can be recommended after a medical and nutritional assessment. Neither diet should be started “on a whim”, and would benefit from advice from professionals like a Registered Dietitian.
Interestingly, many other powerful diets within the research literature (e.g. the Mediterranean diet) incorporate the best features of a Vegan diet with a higher margin of safety. Many clinical diet regimens will encourage a reduction in carb and saturated fat portion size, alongside more nutrient-dense (less processed) food choices. Even for these diets, however, consultation with a dietitian or health professional is recommended.
Resources for Alberta Residents
People who live in Alberta, Canada can access a Registered Dietitian for free through their local Primary Care Network (PCN), typically by asking their family doctor for a referral. In many cases, you will be referred to a Registered Nurse for lifestyle review & coaching prior to your dietitian appointment.
(1) Bueno, N. B., de Melo, I. S. V., de Oliveira, S. L., & 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), 1178–1187.
(2) Seidelmann, S. B. et al. (2018). Dietary carbohydrate intake and mortality: a prospective cohort study and meta-analysis. The Lancet-Public Health, 3(9), 419-428.
(3) Turner‐McGrievy, G. M., Barnard, N. D. and Scialli, A. R. (2007), A Two‐Year Randomized Weight Loss Trial Comparing a Vegan Diet to a More Moderate Low‐Fat Diet. Obesity, 15: 2276-2281. doi:10.1038/oby.2007.270