Quick Summary tl;dr
The main reason why people lose weight on a ketogenic diet is well established: With stabilised glucose levels and low insulin levels, you will naturally eat less and your body will release and burn body fat for fuel.
Apart from anecdotal claims, there is no scientific evidence that high levels of ketones will guarantee enhanced fat loss. If you want to lose body fat, you need to stay in calorie deficit so you can use your body fat for fuel.
Typically, high ketone levels are desirable for therapeutic purposes or top-level performance rather than weight loss.
A low-carb diet is, indisputably, one of the most effective ways to lose excess body fat. Over and over again, studies have proven the myriad benefits of carbohydrate restriction. Being fat-adapted brings several advantages, as you have access to your biggest fuel tank — body fat.
If humans weren't able to burn fat and at some point also ketones as a by-product of fat oxidation, we probably wouldn't be here any more. Tapping into our glycogen stores — yielding approximately 450 Kcal — wouldn't get us very far if we couldn't access the 50,000+ Kcal (in many people this is a lot more!) stored as fat.
Do More Ketones Enhance Fat Loss?
Contrary to what you may have heard, high levels of ketones will not guarantee enhanced fat loss. When you are in ketosis, the level of ketones in your bloodstream won't tell you how much fat you are burning. It will only tell you how much energy you currently have in your "fuel tank". Your body continuously produces and consumes ketones and over time, it will adapt and optimise the level of ketones in your body.
Let's look at the evidence. This review of studies found a correlation between fat loss and the level of acetone, one of the ketone bodies that can be measured with a breath ketone meter. However, studies that are listed in the review compare the effects of a standard low-fat, high-carb diet to a high-fat, low-carb diet. As we know from several studies, low-carb diets outperform high-carb diets. However, if we want to see how ketone levels affect fat loss, it would be necessary to compare low-carb diets and effects of different levels of carbohydrate restriction.
High ketone levels over 3 mM (also known as starvation ketosis) may, in fact, slow down fat loss. High ketone levels will likely elevate your insulin levels and as a result block the release of free fatty acids from your cells.
Ketosis is Not Just a Tool for Weight Loss
It's simple: if you want to lose body fat, you need to stay in calorie deficit and use your body fat for energy. A low-carb diet is a great tool that will help you achieve that. With stabilised glucose levels and low insulin levels, you will naturally eat less and your body will release and burn body fat for fuel.
Although losing weight is the most common reason people follow a low-carb or ketogenic diet, it's not the only reason and it's actually not desirable in some cases. Those who use the ketogenic diet for therapeutic purposes such as managing epilepsy or cancer may want to maintain or even gain weight. The same is true for athletes who use a keto diet for top-level performance.
Should I Measure Ketones?
A blood ketone meter, which is the most accurate way to measure ketones, will measure the level of BOHB in the body. A breath ketone meter is another fairly accurate option for those who need to measure their ketone levels.
Ketone levels vary among individuals, especially when we take keto-adaptation into account. Remember, you can learn how much you have in your "fuel tank" but not how much your body is using for energy.
Compared to someone who just started following a ketogenic diet, keto-adapted individuals will likely show a lower level of ketones simply because their body can use them more effectively than in non-keto-adapted individuals.
So, should you measure ketones? As you might have expected, it depends. I rarely measure my ketone levels. I've been following a low-carb diet since 2011 and I know what to eat and avoid to stay on track. Below I list the most common cases when measuring and tracking your ketone levels can be useful.
New to a Low-Carb Diet
If you just started following a ketogenic diet, measuring your ketone levels can be useful. Just like tracking and planning your diet, monitoring ketosis will help you avoid common mistakes while trying to stay low-carb.
To find out whether you are in ketosis or to learn how certain foods affect you, you can use a breathalyzer, a blood ketone meter or a blood glucose meter (same meter, just different strips). Don't focus on numbers and don't get discouraged when you see low ketosis readings - there are several factors that affect ketone levels.
Ketogenic Diet to for Therapeutic Reasons
If you use the ketogenic diet for therapeutic purposes (epilepsy, cancer, Alzheimer's, etc.), it's a good idea to track your ketone levels.
Ketogenic Diet for Top-Level Performance
Lastly, measuring ketones can be useful if you want to optimise your exercise - unless you perform at a top level, you don't need to do that.
Exogenous Ketones and Ketosis Supplements
I've been frequently asked about the use and effectiveness of exogenous ketones. Although they are likely beneficial for therapeutic purposes or top-level performance, they are unnecessary for the vast majority of people. I'm not a proponent of exogenous ketone supplements - I've tried them and wouldn't recommend them.
Unfortunately, products with exogenous ketones are marketed as weight loss products and their actual use is distorted. Endogenous ketones - ketones produced by the body as opposed to those that are supplemented - are a by-product of fat metabolism. Supplementing your diet with exogenous ketones will not make you burn more body fat. It simply doesn't work that way.
No matter what others will tell you, there is no miraculous pill or supplement that can do the job for you. If you want to lose weight, just stick with the diet. If you want to boost your energy, you can as well use coffee or MCT oil. If you want to learn more about exogenous ketones, here is a great post from KetoGains that goes into more depth.
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