There's never a shortage of new diets purported to be the cure-all for both weight and health. Of recent popularity is a host of diets recommending a reduction in carbohydrate consumption, one of which is the ketogenic or keto diet.
What is a ketogenic diet?
A ketogenic diet relies on an extremely low intake of carbohydrate. This causes the body to shift from using carbohydrate as its main source of fuel, to using fat. The body converts fatty acids into ketone bodies which are then used as an energy source for the heart, brain, and muscles.
As levels of ketones rise in the blood, the body enters a metabolic state referred to as ketosis. The purpose of the ketogenic diet is to get the body into this metabolic state and remain there; utilising fatty acids as energy with the overall goal of reducing the body's level of stored fat.
What is extremely low carbohydrate intake?
Around 5% of your total calories. On a 2000 calorie diet that's approximately 20-25g. To put things in perspective, a 250g punnet of strawberries will get you close to your limit.
Protein intake should be around 25% of total calories and fat approximately 70%. So a 2000 calorie diet would contain approximately around 25g of carbohydrate, 125g of protein, and 155g of fat (fat provides more calories per gram).
Does it work?
In short, "yes but...".
Nothing in nutritional science is ever that simple, and like any diet there are trade-offs.
To digress, anyone who says a particular diet is the perfect solution to human health is jumping the gun. Nevertheless there is plenty of evidence to back some of the purported benefits of a ketogenic diet.
Numerous studies have shown ketogenic diets to be beneficial for weight-loss [1, 2]. With some research indicating that a ketogenic diet may be better for weight-loss than a low-fat diet .
We know there is a greater effect on fat loss when consuming a higher protein diet compared to a lower protein diet, if calorie intake is equal. This is mainly due to differences in muscle mass preservation and the thermic effect of food (TEF) .
If the notion that "a calorie is a calorie" is in fact true, then that should mean the breakdown of calorie intake from fat and carbohydrate beyond protein should not matter. However, proponents of the ketogenic diet suggest a "metabolic advantage" in having most (if not all) of the remaining calories coming from fat . Beyond metabolic advantages, other possible benefits of a ketogenic diet on fat loss may be due to differing levels of satiety and reduced food choices.
However it is worth recognising that weight-loss is not the same as fat loss. The body stores around 500g-700g of carbohydrate (in the form of glycogen) in the muscles and liver, and each gram is stored with approximately 3g of water. On a low-carbohydrate diet, glycogen and water is lost rather quickly, creating a sense of weight-loss that does not equate to fat loss . With that being said, the greater weight-loss from low-carb diets (when compared to low-fat diets) sometimes outweighs possible differences in glycogen retention, and greater fat-loss has also been observed; although to a lesser degree than differences in weight-loss .
Research has also uncovered other benefits of a ketogenic diet beyond weight-loss. It appears to be a viable option to reduce the risk of lifestyle diseases such as cardiovascular disease [1, 7]. Although research is somewhat inconclusive, with some results showing a negative impact on low density lipoprotein (LDL) cholesterol .
Further to that, ketogenic diets have also been shown to reduce the incidence of seizures and protect from cognitive impairment in those suffering epilepsy [9-11]. Other research has explored keto's effect on reducing the rate of tumour growth .
Whilst some research has shown decent compliance to a ketogenic diet, it may not be so easy for some individuals. Given the very low intake of carbohydrate required, it means that social functions are harder to navigate, alcohol consumption is close to off the cards, and more attention has to be paid to planning meals ahead of time.
Further to this, several food groups need to be cut from the diet including grains, legumes, fruit, and starchy vegetable such as pumpkin. All of these foods are a rich source of vitamins, minerals, phytonutrients, and fibre. Given the benefits of many plant compounds (such as phytosterols, antioxidants, and soluble fibre) on cardiovascular health - and overall wellbeing for that matter - there is reason to be wary of cutting such foods from the diet [13, 14].
The evidence of a low-fat, plant based diet in improving levels of health markers (such as blood lipid profile) as well as eliciting weight-loss, is also well established [8, 15, 16]. It may seem counter-intuitive that both a low-carb and low-fat diet can have a positive impact on health and weight, however that is certainly what the data suggests. This is evidence of the complexity of nutritional science; there is certainly more than one way to skin a cat, and there are always trade-offs with any food or diet.
There is also something to be said for the enjoyment many people get from consuming the foods that are absent in a ketogenic diet. Food psychology and the potential for disordered eating can never be left out of such discussions, and if cutting out food groups has a negative effect on ones relationship with food, then this may outweigh any possible benefits of a diet.
There is plenty of evidence to suggest that a ketogenic diet can improve health and aid in fat loss. That fat loss may be more substantial than what is seen on low-fat diets due to a higher protein intake and the possible "metabolic advantages" of using fat as a primary fuel source.
However, the very low intake of carbohydrate and removal of many food groups may make adherence hard for some people. Given that there is ample evidence of benefits to body fat mass and health from diets with a higher intake of carbohydrate, such individuals should look to one of these diets as an alternative.
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