Do I Need to Eat More Fat to Burn Fat – Q&A
Question: I’ve often seen it claimed that one needs to ‘eat fat to burn fat’ and that this is one of the advantages of low-carbohydrate diets. But, like so many myths in the diet world, I’m wondering if this is actually true. Is it?
Answer: The short answer, as you might have guessed is no. Now, as always, here’s the longer answer.
I suspect that the idea that one needed to eat fat to burn fat came out of a misunderstanding of some of the early literature on low-carbohydrate/high-fat/ketogenic diets (note: I’m defining a ketogenic diet here as any diet that contains less than 100 grams of dietary carbohydrate; a topic discussed in more detail in my first book The Ketogenic Diet).
In those studies, there was clearly an increase in the body’s use of fat for fuel (indicated by a large scale decrease in something called the respiratory exchange ratio or RER) and I have a hunch that people assumed that it was the huge increase in dietary fat that was driving the increase in fat burning.
But as I discussed in Nutrient Intake, Nutrient Storage and Nutrient Oxidation as well as in How We Get Fat, the burning (oxidation) of fat isn’t really related to fat intake per se. Rather, it’s related to carbohydrate intake. That is, the act of eating dietary fat doesn’t usually have a major impact on how much fat you burn. I say ‘not usually’ as some studies find that very high fat intakes (like 80 grams all at once) have a small effect on fat oxidation by the body. But for the most part, how much fat the body burns during the day is related primarily to carbohydrate intake, secondarily to protein intake, and almost not at all to dietary fat intake itself.
Also consider that the following three conditions:
- Complete fasting (no food intake at all)
- A high-fat, low-carbohydrate ketogenic diet (e.g. 30% protein, 65% fat, 5% carbohydrate)
- A protein sparing modified fast (PSMF, such as my own Rapid Fat Loss Handbook)
All generate basically the identical shift in the body’s fuel utilization: a decrease in resting RER indicating a shift to using predominantly fat for fuel. Again I say basically since both the ketogenic diet and the PSMF will be marginally different than complete fasting due to the intake of dietary protein. But for the most part, the shift in fuel use by the body is identical in all three conditions, you see a huge drop in RER indicating a massive increase in the use of dietary fat for fuel.
And the commonality in all of those conditions is not the presence or absence of dietary fat (diets 1 and 3 have little or no dietary fat, diet 2 has quite a bit). Rather, it’s the lack of dietary carbohydrates. Which, based on what we know about how the body determines fuel usage makes sense. As I discussed in the linked articles above, when you eat more carbs, you burn more carbs (and less fat); eat fewer carbs and you burn fewer carbs (and more fat). Which means that in all three conditions above it’s the absence of dietary carbohydrates driving the increase in fat burning, not the presence of dietary fat.
Which isn’t to say that increasing dietary fat intake under some conditions can’t have benefits (such as increased fullness, food enjoyment or flexibility, limiting the daily deficit to moderate levels if that’s the goal, etc.) which are discussed in other articles on the site (I’d suggest the Comparing the Diets series for an overview of different dietary approaches). It’s simply that increasing fat burning per se simply isn’t one of them; rather, that’s accomplished by reducing carbohydrates and total caloric intake.
Hope that answers your question.
Hi Lyle!
Great article, like always yeah!
I have a question refered to burning fat or carbs, depending on how much we eat.
Now I’m following the recomendations of your article “How many CHO do you need?”, and in this way I’m consuming 50g to limit protein breakdown and another 75-100g to do my workout. I eat around 220g of protein (180g of wich are from animal source) and roughly 80g of fat. I weight 67-68kg, and don’t know if I’m doing well. My doubt refers to the burning of fat, I’m consuming more fat than carbs, but in addition I’m consuming more protein than fat and carbs, and I don’t know if it could affect the idea that if we consume less carbs we will burn more fat. Can you orient me?
I have another questions,sorry jejeje,but I think it’s more simple; always when refered to the quantity of protein in fat loss or in gain muscle you talk about 3 or 3’3 g/kg, but I don’t know if it’s from lean body mass (in one article you said this, but in another you didn’t mention anything and I’m confused) and if you are talking about animal source or the total of protein intake, although I think it should be a ratio between protein and vegetal source no?
Thank’s for all Lyle, don’t stop doing this fantastic job!
My best regards, Víctor
Oh sorry, I forgot to say that with my macronutrient intake I want to note that I’m consuming 2200kcal aprox on day, but with the recommendation of consuming about 3 to 3’3g/kg of protein to not allow protein breakdown, it means that I consume more protein than fat and carbs, and I have read in your article “how we get fat” that if we consume more of one macronutrient we will burn more of it and less of others (fat and CHO) and because of it I don’t know if I I’m doing well with this quantities of macronutrient. I don’t know if it’s better to reduce CHO and eat more fat… on the basis to eat only the necessary CHO to train properly; or reduce a little bit the intake of protein.
I want to lose fat & I want to do it as well as I can.
Hope you can help me
Thanks!
Clearly eating more fat is different from eating a higher proportion of fat- if calories don’t increase, then as fat increases, carbs decrease, leading to diminished glycogen stores and feedback mechanisms via pyruvate dehydrogenase to decrease oxidation of pyruvate, preserving carbohydrate stores (or at least the end product of glycolysis before it enters the TCA cycle). At least this is part of that regulatory mechanism, and there are others as well. But this explains why just eating more fat isn’t effective- as long as glycogen stores are fully maintained, there’s little need to burn fat, and the body preferentially tries to dispose of excess carbs. The same might be true for excess protein, especially short chain amino acids that are easily deaminated and enter the TCA cycle, though I haven’t looked into this. Any idea?
Thanks for the article. I often refer people to your site.
Hi,
As you know RER is also associated with activity level…when there is a decrease in RER with lower carbohydrate intake, is this adjusted for activity level? Are people reducing activity level (conscious or NEAT) with lower carb diets?
Hi, are you still taking questions? I am getting so many different answers from different websites I don’t know where to turn.
I ve been doing the ketogenic diet for almost two weeks and insead of losing weight (eventhough it is water) I have gained 4lbs. My pre-keto weight was 120 and consumed 1400 calories as you recommend did my workouts . I know I m in ketosis bc of the keto sticks but why the weight gain? Before this diet I being on the paleo diet (low carb diet) . I do CF 5 days /week and sometimes I add 15 mins of low cardio workout. My body fat percentage is 28.9 . Do you think this diet if for me? Should I continue with the diet ? Thanks in advance for your help.