What is a keto diet?
The ketogenic diet or “keto” diet is a very high fat, moderate/low protein and low carbohydrate diet. The carbohydrate content of the diet is usually below 50g per day. Although not a new diet, the ketogenic diet has rose to prominence again and has often been hailed as the best way to lose fat. Carbohydrates and fats are the two main sources of fuel for the body. When you consume carbohydrates, they become your bodies preferred fuel source. However, consuming very little to no carbohydrates forces the human body to switch to fat as the preferred fuel source. This then produces ketone bodies (a process known as ketosis). The ketone bodies can then fuel your brain and muscle in the absence of carbohydrates (glucose to be more specific). This is again an excellent example of what I have talked about previously about our body being pretty good at adapting to different stresses.
Is a ketogenic diet superior for burning fat?
Although placing the body into ketosis does burn more fat as fuel that does not equate to fat loss. As I mentioned before your body will use the fuel source that is available, if you are eating a lot of fat in your diet then of course you will be burning more fat as a fuel source. Whereas if your diet is predominantly carbohydrate you will burn more carbohydrates as a fuel source. Again, this does not equate to actual fat loss. That will be determined by whether you are in a negative energy balance (a calorie deficit) or not.
Is a ketogenic diet superior for fat loss?
Not according to the overall body of evidence that we have. Some studies have shown benefit of lower carbohydrate and some studies have shown benefit of lower fat. When calories and protein are the same between both groups the percentage of fat and carbohydrate doesn’t seem to make a significant difference to overall fat loss.
Why do I hear about people losing weight quickly on a ketogenic diet?
You often see quite rapid weight loss in the first week or so on a ketogenic diet. However in reality, most of the weight lost during this time is water. Your body stores carbohydrates as glycogen and for every gram of glycogen stored there is 2.7g of water stored with it. Once you start restricting carbohydrates, your body will lose the glycogen that’s stored along with the water that it holds.
It may sound like I am completely hating on a ketogenic diet here, but I am not, it’s just the overall evidence we have doesn’t show that it’s superior to other diets long term when matched for calories and protein. For any fat loss diet to work it must adhere to energy balance. You will not lose fat if you are taking in more energy in the form of food than what your body is using, this includes the ketogenic diet. However, If the ketogenic diet is something that helps you achieve a calorie deficit and is something that you feel is sustainable and fits your lifestyle better by all means do it. It just isn’t magic.