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:

  1. Complete fasting (no food intake at all)
  2. A high-fat, low-carbohydrate ketogenic diet (e.g. 30% protein, 65% fat, 5% carbohydrate)
  3. 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.

Comments

comments

10 thoughts on “Do I Need to Eat More Fat to Burn Fat – Q&A

  1. 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

  2. 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!

  3. 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.

  4. 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?

  5. Hi, are you still taking questions? I am getting so many different answers from different websites I don’t know where to turn.

  6. 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.

  7. Great articles & information on this site!
    Could you give more information on increasing dietary fat intake for metabolic flexibility?

    Thank you!

  8. Bullshit. Eating fat, makes you loose fat. If tha’s not true, how the hell me and my clients got a better body recomp?
    You talkin bro-science, brah?

  9. No, I’m talking real science, the science behind nutrient oxidation and what impacts it. Eating more fat doesn’t affect fat oxidation unless you eat an absolute ton of it (and you still store way more than you burn). Eating less carbs does. You’re the only one talking bullshit, my friend and every physiology book, paper, etc. in the history of ever will show you that.

  10. Some real science, missit

    ***
    tr. 1993 May;57(5 Suppl):759S-764S; discussion 764S-765S.
    Food quotient, respiratory quotient, and energy balance.
    Westerterp KR1.
    Author information
    Abstract

    This paper reviews evidence that the macro-nutrient composition of the diet and the maintenance of energy balance are correlated. Intervention studies show that subjects lose weight on low-fat diets and gain weight on high-fat diets. Descriptive studies show that overweight subjects eat relatively more fat but have the same total energy intake as nonoverweight subjects. The body has a limited ability to oxidize fat compared with its ability to oxidize carbohydrate and protein. The conclusion is that becoming overweight can be prevented by reducing the fat content of the diet. Studies on nutrient utilization show a ready increase in carbohydrate oxidation whereas fat oxidation does not change after meals enriched with, respectively, carbohydrate or fat. However, in the long term, the respiratory quotient (RQ) is closer to the food quotient (FQ) for subjects eating high-fat diets than it is for subjects eating high-carbohydrate diets. For high-carbohydrate diets, the RQ is lower than is the FQ, indicating that subjects must mobilize body fat. This is supported by data on body weight loss in subjects changing from a standard maintenance diet to a low-fat diet, even while energy intake was increased with nearly 20%. Direct evidence for a higher energy expenditure for low-fat diets is not yet available.

    ***

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    J Am Coll Nutr. 2010 Aug;29(4):343-51.
    Body fat regulation: is it a result of a simple energy balance or a high fat intake?
    Pereira-Lancha LO1, Coelho DF, de Campos-Ferraz PL, Lancha AH Jr.
    Author information
    Abstract

    The search for the causes of obesity has involved genetic abnormalities and endocrine and neural lesions. Although evidence suggests that genetics plays an important role in body weight regulation, rapid increases in obesity rates do not seem to be caused by significant genetic changes within populations. Total energy expenditure and total energy intake are not the only factors that regulate body fat. Nitrogen and carbohydrate balances are eased by the capacity of the organism for adjusting amino acids and glucose oxidation rates, respectively. Regarding fat, this mechanism is considerably less precise; a fat intake increase does not stimulate its oxidation on the same basis. In addition, dietary fat is stored very efficiently as body fat. Elevated carbohydrate ingestion enhances glycogen reserves, which usually are much smaller than the maximum capacity of storage and enlargement of these stores, thus stimulating this nutrient’s oxidation. These data point to a very well controlled carbohydrate balance in the body. Various studies show lack of efficiency of the hyperlipidic diet in stimulating satiety. Signals arising from the gastrointestinal tract play a fundamental role in regulation of appetite and energy intake, and evidence indicates that the gastrointestinal and hormonal mechanisms involved in the suppression of appetite and in energy intake are compromised in obesity. A high-fat diet is important in its origin. Additional studies are necessary to explain the mechanisms that lead to adipose tissue retention resulting in a fat-rich diet.

    ***
    Clin Nutr. 1995 Apr;61(4 Suppl):952S-959S.
    Use and storage of carbohydrate and fat.
    Flatt JP1.
    Author information
    Abstract

    Starch, sugars, and triglycerides provide the bulk of dietary energy. To preserve homeostasis, most of the glucose and fat absorbed must be stored to be mobilized later at rates appropriate to bring about the oxidation of a fuel mix matching on average the macronutrient distribution in the diet. The body’s glycogen stores are so small that regulatory mechanisms capable of efficiently adjusting carbohydrate oxidation to carbohydrate intake have developed through evolution. Fat oxidation is regulated primarily by events pertaining to the body’s carbohydrate economy, rather than by fat intake. Adjustment of fat oxidation to intake occurs because cumulative errors in the fat balance lead over time to changes in adipose tissue mass, which can substantially alter free fatty acid concentration, insulin sensitivity, and fat oxidation. Fat intake and habitual glycogen concentrations are important in determining how fat one has to be to oxidize as much fat as one eats.

    ***
    Bottom line, eating fat doesn’t stimulate fat oxidation. That’s the real science.

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