The keto misconception
Yes, the ketogenic diet is perhaps more effective than any low-fat or inherently energy-deficient diet when it comes to losing weight. But as we’ve touched on, when you remove the independent effects of weight loss, it becomes difficult to clearly demonstrate any additional benefit.
Metabolic ward studies carefully controlling for overall energy intake and matching for protein have clearly demonstrated that people burn more fat on a keto diet (high in fat), but do not actually lose any more weight or body fat than on a low-fat high-carb equivalent diet. When calories and protein are equal, the keto diet does not clearly offer any metabolic advantage. When we standardise everything and compare a keto diet to a low-fat diet of the same caloric intake, there’s no consensus that there’s any additional benefit in terms of body fat loss. You absolutely see clear increases in fat oxidation on a keto diet as you would expect, but a common misconception is that this translates to a reduction in body fat. When people think about a ketogenic diet for weight loss, it’s sold as creating more fat loss because of this metabolic advantage that you’ll burn your own body fat as a product of you putting your body into starvation mode. But while it’s true that on a ketogenic diet you’ll be burning more fat, you’re not necessarily melting away your own internal fat. In reality, you’re simply adjusting to the fact that you have a higher fat intake because you’re displacing carbohydrate. The carbohydrate-insulin model predicts that a low-carb diet will elevate energy expenditure, and experimentally there is a suggestion that metabolic rate is increased on a keto diet. However the magnitude of this increase is just about detectable with the methods we have to measure it, and the assumptions used in the calculation of energy expenditure (e.g. the doubly labelled water method), may actually lead to some overestimation. In any case, how this independently contributes to any additional energy deficit has yet to be demonstrated. There is some suggestion that there are slight metabolic differences around blood lipids on a ketogenic diet, too – with improved ability to clear blood lipids from the system after a meal, plus the proposal of increased levels of HDL cholesterol (the good kind). But these blood lipids might not always be favourable, so you could be better at clearing lipids from the system, but you might have unfavourable changes to blood cholesterol like LDL (the bad kind). Whether this is larger lighter LDL (less bad) is unclear. Obviously blood glucose levels are lower on a keto diet on average across a day, mainly because you won’t have influxes of glucose from the diet anymore. As a consequence, insulin levels also remain low. Things to consider before starting
Restricting carbohydrates to 50g or less can be challenging given the fact that carbs are found in most foods. This restriction can limit food choice and it’s important to remember that maintaining a low-carb intake isn’t always easy – for some inspiration, check out Form’s low-carb smoothie recipes.Following a low-carb diet doesn’t guarantee you are in ketosis constantly, and your metabolic state may fluctuate with just slight adaptations to carb intake. Is this a problem? Well, yes and no. No in the sense that a low-carb diet even with periods of ketosis can be beneficial, but yes in that if you are maintaining a high-fat intake and fail to reduce carbs then there can be ill effects of a high-fat intake – failing to lose body fat and potentially contributing to health risk in the long run.You can still eat too much and eat “crap” on a low-carb diet. The food industry has cottoned on to the popularity of low-carb and keto diets and has now started to offer indulgent foods to meet this market. Hence you can still eat unhealthy, highly palatable foods on a low-carb diet, which might mean you may not necessarily get the reduction of calories often observed.
References/further reading  Ketogenic diet and adipose tissue inflammation—a simple story? Fat chance!  Low-carbohydrate ketogenic diets, glucose homeostasis, and nonalcoholic fatty liver disease  Low-carbohydrate diets for the treatment of obesity and type 2 diabetes  A review of the carbohydrate-insulin model of obesity  Energy expenditure and body composition changes after an isocaloric ketogenic diet in overweight and obese men  Long-term ketogenic diet causes glucose intolerance and reduced β-and α-cell mass but no weight loss in mice