Sep 01 2020

Review of Keto and Intermittent Fasting

A new review of the published literature regarding the ketogenic diet and intermittent fasting has, from my perspective, entirely predictable results. By this I mean they are consistent with previous dieting research and there are no surprises. They are also consistent with one of the major themes of this blog – you cannot get away from fundamental realities by making cosmetic changes. You cannot change the laws of physics or the nature of biology. This often translates to the fact that, as a general rule, there are rarely easy or simple answers to complex problems.

When it comes to dieting, researchers generally focus on several basic outcomes – weight maintenance, heart health, and glucose metabolism. You can also look at overall health outcomes, such as the risk of death over time. In terms of weight, there is only one factor that seems to matter – calories in vs calories out. This is the unavoidable reality, and there does not seem to be a way to game the system to significantly alter this equation. Proponents of special diets will argue that varying the proportion of macronutrients (fat, protein, and sugars) can affect metabolism. Some ironically argue that their recommended macronutrient balance will make metabolism “more efficient”. This is not necessarily a good thing when it comes to weight, however. Efficiency could mean getting more use out of fewer calories. If you want to waste energy (i.e. fat) you want to be inefficient.

But the bottom line of decades of research is that any effect of diets that vary macronutrient ratios on metabolism seem to have an insignificant effect on weight. You simply cannot get away from the massive factor of calories in vs calories out by slightly tweaking metabolism.

What does this current review show? Exactly that. First they find, as with most prior research, that the two diets do result in short-term weight loss. Pretty much all diets do. However, they also found that long term research (meaning up to 12 months) show that any short term advantage is lost and not sustainable. Since the goal of weight management is long term control, a short term reversible and small advantage does not contribute to this goal. It may, in fact, backfire. It is a distraction from effective long term behavioral changes. And some studies show that the rebound weight gain is greater. The review also concludes that any short term weight loss may be due to simply reducing calories, not any metabolic change. That is still the overall conclusion of the totality of dieting research – that any observed weight loss is due to reduced calories and not some other factor.

So for weight management, long term sustainable behavioral changes is key. Fad diets do not provide any long term advantage, and may ultimately be counter-productive.

What about heart health? For the keto diet, which involves very low carbohydrates, there has always been a concern that the increased fat in the diet would be harmful. Here, the literature is very mixed. Weight loss itself may be more protective than any increased risk from increased fat intake. Also, you can mitigate the negative effects of increasing fat if that fat is “healthy” fat, meaning unsaturated vegetable fat. But again, long term, since the weight loss is not sustainable, there may be an overall disadvantage, and some research does show in increased risk of death on the keto diet.

The authors of the review also bring up another important point – how generalizable are the results of this research? This is always a good question, but here they have a specific worry. In studies of low keto diets, they can control what fats subjects eat and make sure they consume healthy fats. In the real world, however, outside of clinical trials, people are not likely to stick to only healthy fats, and may also increase their intake of saturated animal fats. So as a public health intervention, the recommendation to eat a low-carb diet will likely have the unintended consequence of increasing the consumption of unhealthy fats.

With regard to glucose metabolism, there does seem to be advantages in the keto diet, which is to be expected. Keto is a low carbohydrate diet, so of course carbohydrate metabolism will be eased in diabetics who have difficulty metabolizing carbohydrates. The real question is – is a keto diet any better than a standard diabetic diet, which is low carb, replaces simple sugars and white starches with brown starches, but is not designed to induce ketosis? There is no evidence of any advantage to keto, and there is also no reason to think there would be one.

There is less evidence overall for intermittent fasting. Again, the authors conclude that any weight loss is due ultimately to calorie restriction. Their concern is that fasting will increase hunger, and may lead to binge eating and eating unhealthy foods. Their main recommendation is for more clinical research.

In the end we are left where we always have been. The best advice is for calorie control through overall healthy behaviors, such as portion control and avoiding large amounts of high caloric and low nutritional food. Eat a varied diet, everything in moderation, and make sure you get plenty of vegetables. Be physically active. These basic lifestyle factors are 99% of the game. I feel like all the fad diets are fighting over the 1%. Forget it – focus on the 99%.

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