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Did a low fat diet beat a low carb diet for fat loss?

A story emerged on March 5th 2015 from the annual meeting of the Endocrine Society in San Diego. It was not widely covered, but James Gallagher, Health Editor for BBC online, wrote about it here and The Times picked it up (firewalled).

The study

The study presented at the conference was undertaken by Kevin Hall and colleagues working in Maryland, US. Hall has done some brilliant mathematical work looking at the 3,500 calorie formula.

The purpose of this study was to see if restricting fat or restricting carbohydrate, by the same number of calories, would have more impact on body fat lost.

The study involved 10 men and 9 women who were obese. The average age of the participants was reported as 24 in one part of the briefing paper that I saw and 34 ± 2 in another part. The average BMI was 36.

The participants were contained in a metabolic ward during the study, making this far more rigorous than any ‘free-range’ study, where subjects are expected to stick to a diet from home/work. For 5 days the subjects were given “the exact number of calories they needed to maintain their body weight” in the composition of 50% carbohydrate 35% fat and 15% protein. (This is slightly different to the US guidelines to have 55% carbohydrate, 30% fat and 15% protein, but the study was not designed to test current guidelines.)

For the following 6 days, the participants were randomly assigned to one of two groups where they received a 30% reduced-energy diet by having either their fat or carbohydrate intake restricted. Two to four weeks later (to allow everything to settle back to normal after the first experiment), the participants were readmitted and they repeated the same 5-day diet to maintain weight: 50% carbohydrate 35% fat and 15% protein. Those who had done the 6-day reduced fat diet in the first phase were put on the reduced carbohydrate diet, and those who had eaten the reduced carbohydrate diet were given the reduced fat diet.

This was what we call a “cross-over” trial therefore – all subjects did both interventions. This is an ideal design for this kind of short-term intervention, as it overcomes individual differences of some subjects responding better to one intervention or another. Everyone tried both interventions and so the individual responses are much compensated for.

The results

The results were presented as “Compared to the reduced carbohydrate diet, the reduced fat diet led to a roughly 67% greater body fat loss.” Wow – 67% – how impressive is that? Completely unimpressive as it turns out…

The calorie requirement established during the first five days of 50% carbohydrate, 35% fat, 15% protein was considered to be 2,720 ± 50 calories. This would be my first challenge. My weight is stable and yet my calorie intake is different every day to the next. I don’t see how a fixed calorie intake number can be established at all, let alone in five days.

Notwithstanding this, the study reduced calorie intake by 30% for the subjects for the next 6 days – the reduction to either come entirely from fat intake or entirely from carbohydrate intake.

If someone is having 2,720 ± 50 calories in the percentages 50% carbohydrate, 35% fat, 15% protein, they are having 1,360 carb calories, 952 fat calories and 408 protein calories. The study reported removing 790 ± 20 calories from both diets – all of these to come from carbohydrate intake for the LC group and all 790 ± 20 calories to come from fat in the LF group. This resulted in the following balance of macro nutrients:

The LC group ended up with a diet comprising 30% carbohydrate, 49% fat, and 21% protein.

The LF group ended up with a diet comprising 72% carbohydrate, 7% fat, and 21% protein.

The problems

You can immediately see one of the problems. This should have been called RC and LF – Reduced Carb and Low Fat. The fat intake at 7% is absurdly and unnaturally low; the carb intake at 30% is way higher than any genuine low carb diet. Hence this was not comparing a low carb with a low fat diet. It was comparing a reduced carb diet with an unnatural fat intake.

The body fat loss for the 6-day intervention was calculated as 394 grams for the low-fat group and 236 grams for the reduced-carb group. The difference is 158 grams – about the weight of an apple. However, 158 grams divided by the smaller of the 2 numbers (236) = 67% and that’s where the 67% comes from.

Even more disingenuous is the method of calculation. I wondered how body fat lost could possibly even be calculated to that degree of accuracy (because it can’t). The briefing paper shared the methodology: “The researchers measured the amount of fat eaten and the amount of fat burned, and the difference between them determined how much fat was lost from the body during each diet.”

What?! The researchers have assumed that dietary fat has no other use within the body – any eaten needs to be burned and that’s all that can happen. That is a completely invalid assumption. Fat is the most versatile macro nutrient to the body. It can be used for energy and it can (and is) used for the maintenance and growth of every cell in the body.

The low fat group consumed hardly any fat during their intervention – 135 calories of fat daily, which is about 15 grams. The reduced carb group maintained the same fat intake as in the weight maintenance phase – 952 calories = 106 grams. There was a 91 gram difference in daily fat intake. If we average the grams of fat claimed to have been lost over the 6 days, the LF group allegedly lost 66 grams a day and the RC group allegedly lost 39 grams a day. But the difference is more than three times accounted for by intake.

The low fat group consumed barely any dietary fat to be used for cell maintenance and repair. The entire fat intake of the restricted carb group could have been used up in body maintenance and growth.

Even if the calculation is as simple as grams of fat eaten – grams of fat burned = grams of fat lost, and it isn’t, we can reverse engineer the numbers to show that the reduced carb group were burning 145 grams of fat a day vs. 81 grams of fat a day being burned by the low fat group. So the headline could have been “reduced carb diet burns almost twice as much fat as low fat diet.”

Weight loss vs. fat loss

The headline could also have been “reduced carb dieters lost 46% more weight than low fat dieters”. This was a finding of the study – the average weight loss with the reduced carb diet was 1.9kg in 6 days; the average weight loss with the low fat diet was 1.3kg in 6 days – that’s a difference of 46% if you want to play the misleading relative numbers again. A genuinely low carb diet (under 10% carb intake) could have achieved a 2-3kg loss in 24 hours, as approximately 500g of glycogen would have been depleted and approximately 2kg of water along with it.

Where does this leave us?

The briefing paper did at least acknowledge: “Long-term extrapolation of our results is fraught with difficulties.” However, this didn’t hold the researchers back from the conclusion: “While fat oxidation during prolonged LF and LC diets would be expected to slowly wane over time, our data suggest that the greater fat imbalance is likely to persist with the LF diet leading to more long-term body fat loss than with the LC diet.”

Hall also shared with James Gallagher the challenges of the diet – even in just six days: “It’s not easy, these folks had to eat the same meals every day. This was very strictly controlled and they had to eat the food provided and nothing else, the diets got pretty boring pretty quickly.”

Could a 7% fat diet be done ‘free-range’? Highly unlikely. Should it be done ‘free-range’? Absolutely not. The reality is that a diet with 72% carbohydrate intake and 7% fat intake is unhealthy in the medium, let alone long, term. It would not deliver the essential fatty acids and fat soluble vitamins, A, D, E and K, so vital for human health and survival, let alone the macro nutrient requirements for body maintenance and repair.

While this was a well designed and controlled study, therefore, it is difficult to see how this leaves us with anything useful to take away. Surely the time would have been better spent studying a diet that could actually be recommended and sustained, if shown to be of any benefit, and to report results more scientifically than a headline-grabbing relative risk based on an invalid assumption that comes down to the weight of an apple.

34 thoughts on “Did a low fat diet beat a low carb diet for fat loss?

  • Some of the supplements:
    Combo of overweight, high sodium intake speeds cell aging in teens
    (including 1 comment)
    Hunter-Gatherer Energetics and Human Obesity
    (including comments)
    Hard Evidence: what do primary school children need to eat?
    (including comments)
    Ethics of embryo editing divides scientists
    (including comments)
    Why nutrition is soconfusing
    But where is the real science of salt? Only in traces.

  • Dear Zoe, why do you write nothing about the salt, although this the real problem in our diet?
    The unnecessary sodium salts increase the incidence of every illnesses without any exception! We must feed ourselves according to maximum economy principle – but not the disorder – in our every cells. The maximum economy principle can be found in the composition of human milk, which is an evolutionary perfect food (from every viewpoint). Naturally, the composition of the human milk is the perfect guide for adult nutrition (sodium/potassium ratio, ratio between sum of alkaline metals and sum of polyvalent metals, ratio between metals and energy content, etc.).
    The evidences: In the scientific literature & media the salt has political- & a lot of pseudoscience but real science of salt we can find only in traces because it’s really CENSORED globally. It’s time to understand, teach & use some very important but forgotten & ignored knowledge; fundamental natural laws/facts & to see the sad reality. The spontaneous diffusion of Na ions into the cells & the diffusion of K ions out of the cells continuously enhance the entropy (disorder). The task of the Na/K pumps to keep constant the intracellular concentration of Na & K ions. These cellular pumps continuously use energy (ATP). Excess Na intake = excess diffusion = excess increase of entropy = excess work for pumps = excess energy expenditure against excess entropy > excess food consumption. But all the rest of our vital processes (functional processes of the cells) receive less energy because our capacity (to make energy from foods) is limited. Everything work worse in our body & this increases the incidence of all illnesses without any exception, our aging & devolution accelerate etc. this is why Na-salts are perfect foods of entropy. 10th ed. of RDA was the best recommendation ever, 500 mg/day Na! Sugars & fats are foods & are sources of energy. But entropy & Na intakes = five decades global censorship, corruption, pseudoscience & lack of real science. Excess Na intake significantly enhances the entropy because the surface (billions) of cells is extreme large, this is the main risk factor of diabetes 1-2, overweight, NCDs etc. & our devolution is a considerable fact too. The law of entropy is the fiercest enemy of life & is our fiercest enemy too. NaCl isn’t food for humans but is perfect food of entropy. Every mmol excess Na & the wrong Na/K ratio & other wrong ratios increase more the entropy in our every cell, but the specialists talk about these rarely or NEVER. Excess Na intake doesn’t increase the oxidative pathway, but a critical surplus switches the anaerobic glycolysis on, in our every cell & we produce cytotoxic lactic acid. This is the Sodium-Induced Cellular Anaerobic Glycolysis. All of our vital processes & organs work worse (heart, brain, regulating systems, immune system etc.) & our cells are dying. We haven’t enough energy & enough time for the regeneration because we enhance the entropy in our every cell, day by day, again & again. The average lifetime of our cells shortens. Faster the telomeres run out. Our aging accelerates. We get sick often & we will die soon. Logical consequence: the unnecessary salt increases the incidence of all illnesses without any exception! This is the no named Sodium-Induced Disorder Syndrome. The entropy law finds our weak point or points & ravages mainly there, but increases the disorder in every cell in our body. We are no uniform, so other risk factors & circumstances affect the individual consequences. The growing entropy is our number one public enemy on every level; physical & mental health & social level globally. The evolution of life on Earth, our history & our entire individual life is a continuous war against entropy. But we, humans started our devolution = the entropy is growing in human genome. Even we nourish the entropy in our every cell (fundamentals of our existence) but the health scientists don’t talk & write about this. This is really a fatal error. Non-communicable knowledge is too much in salt science, it’s time to change that, because we will die out within 250 years!
    “The Center for Science in the Public Interest in 1978 petitioned the Food and Drug Administration to revoke the generally recognized as safe status and limit salt, … It is unfortunate that government health authorities have not shown the will to act.” Source:
    But the CSPI is weak, because they don’t use the already existing knowledge. This is awesome guilty irresponsibility &/or astonishing ignorance. Optimal ratios & quantities are in human milk. From every viewpoint the human milk is an evolutionary perfect food, including minimal energy expenditure of the Na/K pump & kidney of babies = possible minimum „entropy-transfer” into babies = healthy growing with maximal economy. So, the human milk is perfect guide to calculate optimal adult intakes. But the scientists ignore these facts. The health sciences made experimental animals from the humanity. The entropy is nourished in us with Na-salts, but they don’t talk & write about this. They are treating only the symptoms & consequences of the Sodium-Induced Disorder. Without real salt science – evidence based medicine & really preventive medicine doesn’t exist. Sodium recommendation is bad, education is astonishingly bad, the strategy against obesity, NCDs etc. is bad. True science of salt exists only in traces in the scientific literature, & in some articles even the traces are concealed & censored. In my article on science20 I collected the most important evidences (near 70 references) of the above ones:

  • All this discussion — and the stuff in the media — assumes that we know what happened in this study. Do we? The title and the general drift of the paper implies that low fat reliably has a better effect on fat content than reduced carb. But all that we are given is average outcome and examination of Table 3 shows there is big variability. So, did half the subjects do better on LF. Was it all of them? Was it one or two who has such big changes that they biased the average. Before we analyze this, we should find out. New rule: habeas corpus datorum. Let us have the body of the data. All of it.

    What you want from a diet comparison is not an average. A single dieter cannot be an average. You want to know which diet to bet on, how many people do better on diet A versus diet B.

  • Pingback: Why the New “Low Fat Beats Low Carb” Study Is a Clear Sign of the Apocalypse | Escape From Caloriegate

  • Nice analysis Zoe.

    But even taken at face value and assuming the results are sustained, I don’t see how this refutes Taubes or the carbohydrate-insulin hypothesis of obesity.
    Which seems to have been Hall’s obsession.
    For one thing, no-one was gaining weight, and as far as I can see so far no-one included was very insulin-resistant either.
    Additionally, the way the very low fat arm lost fat had nothing to do with the insulin hypothesis.
    Fat was so low that dietary fat plus DNL was insufficient for the body’s needs (for cells that need to burn fats as well as structural uses); in such a situation hormones such as insulin are over-ruled to ensure homeostasis and survival. Hormones are not the only players in metabolic control and energy substrates such as glucose, fatty acids, and ketone bodies also exert signalling effects; intermediates and products regulate the rate of reactions just as, at a higher level, hormones do – there is considerable built-in redundancy to ensure energy is appropriate for survival in extremis.
    The existence of this sort of failsafe at a metabolic extreme cannot refute any hypothesis about the role of hormones; Taubes can walk away from this one.

    • Nice one back George!
      I don’t think GT is losing much sleep :-)

      • What fascinates me is that the “study” was done 5-6 months or more ago, and Zoe wrote this blog-piece 5 months ago, yet suddenly in the last 2 weeks everyone has woken up and posting it on all sorts of sites. Do we take so long to wake up?

  • Thanks for breaking down this study. It sounded so legit when I first heard about it. I should have done some of the math myself. Most studies do not get the carbs low enough. I hear that from all the experts. Keep up the good work!

  • 6 days??? No one even starts to feel better on a ketogenic diet untill they’ve adapted metabolically by about week 3!
    At the age of 22, when I was still pretty insulin sensitive, I went on a low fat diet, as recommended by my doctor, to treat the non disease of familial hypercholesterolaemia. To my delight I quicly lost 5 lbs, only to put on 20 lbs more over the next year. I was never overweight in my life before that. Oh, and mt triglycerides were through the roof for the first time.

    Contrast that with my attempt to loose weight after my second pregnancy at age 36. After the 3rd week of a ketogenic diet, I felt fantastic and I’m back to the same weight I was at before the disastrous low fat diet, and have maintained that weight (105 lbs on a 5’1″ frame) for the past 15 years. And my triglycerides? The lowest my doctor has seen. So again I say… 6 days???

  • I think this does leave us with something useful.

    As somebody who has found it impossible to do this whole low carb thing (and I did do it properly…several times…each time felt like I was dying and it only got worse) it is very encouraging to know that simply reducing carbs will have at least some effect!

    I used to be anorexic and then bunged on a load of weight, diagnosed with thyroid and adrenal disaster and messed around with various ways to get to a comfortable weight over many months. Nothing worked, and I discovered that much of what appears to be fat is in fact deposits of mucin, or inflamed skin tissue. I wonder how many people have this problem without knowing. No amount of weight loss will make it go away.

    It also turns out that those with thyroid problems need more carbs than those without. This explains why my “happy place” seems to be at about 100-150g carbs a day. Any lower and I sleep all day and get raging migraines. This does not stop even after a month. (Yes, I held out that long!)

    Personally I am less interested in being the perfect example of health and longevity than getting lots of creative stuff done and having a good time :) so I fail on the low carb front but I am glad to know that what I’m doing right now, keeping the carbs well below SAD standards, will still have benefits.

    After being at deaths door with anorexia, I really can’t stress how important it is to not be so insanely perfectionist about our bodies. Sure, the way we live right now is an absolute atrocity, and we ought to be changing that. But getting thinner is not going to treat society holistically, we have to go after hearts and minds and politics to do that.

    Just for anybody feeling inadequate or a failure out there. Find your own way.

    • Hi Xkale,
      I had the same problem until I stopped fearing saturated fat. Once I started eating enough fat to satisfy my bodies caloric needs, I felt great.

  • This reminded me of a recent article I saw:

    The problem I found with it (aside from not truly a controlled study) is that what was being called a “low carb” diet was in fact a *no* carb diet.

    I started eating low carb in April at my nurse practitioner’s recommendation. It is fairly easy to do, I still eat veggies, and I have lost a bit of weight and a lot of bad cholesterol. (My lipid profile is pretty amazing now. And I’m still quite overweight.)

    I admit, I don’t follow the usual advice to break away from even low carb sweets, because that would be much harder for me to do. So maybe I would be lighter still now had I done so. But slow and steady will do.

  • Its not directly related to this article, but a question about greens for maintaining a low carb diet.

    Since reading on your site, its all about the carbs, I have switched to low carb smoothies in the morning. Raw Kale, red fruits, almond milk and doses of nuts, flaxseed etc.

    I then read on your site that you need soluble fats to absorb the vitamins of Kale (I assume this works for Spinach and Broccoli too). Could I add a dollop of ghee in the mix to release these or must the kale be cooked to release these too ?

    • Hi Colin – the almond milk, nuts, flaxseeds all contain fat so you have a delivery mechanism already :-)
      Best wishes – Zoe
      p.s. it’s why granny put butter on veg – it provides a delivery mechanism for the fat soluble vitamins in carrots and greens

  • Well, I am sorry, but your explanation of one problem with the study makes no sense to me. How can you go from the study saying that they “measured…the fat burned” to saying that they assumed all fat consumed was burned? I don’t understand how you came to your conclusions when I have no idea how they measured fat burned.

    Then you wrote, “But the difference is more than three times accounted for by intake.” That is so baffling to me I can’t even ask a question about it.

    Please understand that I agree that the conclusion reached by the study authors is incorrect. However, part of your logic for why they are mistaken is incomprehensible to me. So, I am writing really because I’m frustrated.

    • Hi Nate
      Sorry for the late reply – I missed this one while on hols.

      This is a direct quotation from the paper: “The researchers measured the amount of fat eaten and the amount of fat burned, and the difference between them determined how much fat was lost from the body during each diet.” Their words, not mine.

      I also don’t know how they’ve measured fat burned. That’s not the issue. The issue is that they’ve assumed fat eaten minus fat burned = fat lost. My challenge is – you can’t say that because dietary fat is used in numerous ways by the body and thus “fat used by the body” must be factored in somewhere.

      The headlines were about fat lost. Fat lost, using this wrong assumption is simply taken as fat eaten – fat burned.The low fat group consumed c. 15g daily; the reduced carb group consumed c. 106g daily. The study claimed that the low fat group lost 66g a day and the reduced carb group 39g – a difference of 27g a day – but the two groups started off with a 91g difference. Hence the starting point was more than three times in favour of the low carb group to start with. I don’t know how else to put this.

      I hope this helps
      Best wishes – Zoe

  • Hi Zoe–I just love reading your analysis of these headline studies. You’re like a top notch forensics detective; examining the ‘evidence’ to within an inch of it’s life :-) I’m sure I’m not alone when I say I am extremely grateful for all the work you put into disseminating these so-called ‘conclusions’. I do have a question which I’ve been wondering about: If a person still has weight to lose, should they be cutting down on their fat intake so that their body can use up its own animal fat stores for cells and energy, etc? I’ve lost over 130lbs so far and have used good fats to my heart’s content. But now that I want to make the final push after maintaining for a couple of years, I’m wondering if my body can do without as much fat and live off its own supply until I reach a realistic goal weight.

    Thanks in advance for any help you can give on this question-all the best

    • Hi TeeDee
      Thank you for your kind words and mega congratulations on your weight loss. This video may be of interest to show that it’s not fat that you need to cut to get your body to use it’s own fat – it’s carbs.

      You may like to try LCHF as a final option. We’ve got an article in our club on it but it’s not on open view. This was one of the original resources and it gives the kinds of proportions you’d need to consider to do it properly ( People are surprised by the fact that it restricts protein as well as carb. Check out Tim Noakes Real Revolution and search LCHF – it’s getting huge!

      Hope this points you in a possible direction.
      Best wishes – Zoe

  • Great article, thank you
    really love your stuff zoe
    bought your book on a complete whim and it chnanged my perspective on so many things. I went from a low fat/low carb paleo, losing 100 pounds, told later that it was a crash diet, to a Super strict calorie counting/macro managing diet, weighing Everything
    now with your book and research I’ve learned a lot, and I’ve been sampling ketosis as well lately
    I did have one question; do you think long term water weight loss/glycogen depletion, is unnatural or damaging?

    • Hi Ron
      Great to hear how well you’ve been doing – that’s an awesome result :-)

      I don’t think either water loss/glycogen depletion is unnatural or damaging – not least because they are two mechanisms beautifully regulated by the body if the body is allowed access to clean water and real food.

      Water first – the body will make sure you drink by making you thirsty. Your body functions less well as soon as you start getting dehydrated, so the feedback loop is strong to encourage drinking. Respond with water and not fizzy drinks and all will be well.

      Glycogen is made any time we consume more than c. a teaspoon of glucose (from fruit/veg even) and the body calls upon insulin to turn the excess glucose into glycogen to get it out of the blood stream. You’re highly unlikely, even keto adapted to have no glycogen whatsoever (the muscles will retain theirs longer than the liver to be available to move muscles to run away from wild animals). However, the body can happily (many would argue, more happily) fuel on fat as a keto adapted athlete happily finds. You then don’t have the problem of being limited to about 1400-2000 cals of glycogen – you have potentially tens of thousands of energy units (calories) stored as body fat – even an elite athlete has a few tens of thousands. A far larger store room for an endurance test.

      By maintaining consistently low glycogen stores, you’re not unnecessarily carrying the 4 grams of water that accompany every gram of glycogen (hello puffy carb face!) – your body achieves natural water balance by drinking.

      Hope this helps
      Best wishes – Zoe

        • It’s not – the reference to fizzy drinks means what is commonly referred to as fizzy drinks – cola etc :-)

  • I don’t think this experiment can tell us much of anything. For one thing, a diet lasting only 6 days is too short to be able to come to any kind of conclusions. A 30% carb diet is not a “low carb” diet, but a moderate carb diet; and a 7% fat diet is not only unsustainable, but unhealthy in the long term as well. They need to design studies that have some bearing in the real world; otherwise, why bother?

    In any case, there are already loads of studies in which low carb excels in fat loss.

  • Sorry, this is rather off-topic but I would be grateful for the advice. So… can I follow Phase 1 indefinitely? I really enjoy the strict structure of it, even as a vegetarian. I trust myself a whole lot less at the thought of introducing more foods into the plan.

    Thank you.

    • Hi Mark – yes you can – my only worry would be that you risk developing a (new) food intolerance by having the same things too much/too often. If you can rotate foods as much as you can, this would help – more difficult as a vegetarian, I appreciate.
      Good to hear it’s working for you though!
      Best wishes – Zoe

      • Thanks for the reply, Zoe. Might be a bit too reliant on the natural yogurt to be honest. But rice and veggies, red pepper and onion omelettes, and many varieties of soup all do the trick. Really can’t face even the idea of going back to meat and fish after 3 years, although I could see a few benefits to doing so. Best wishes to you.

        Mark x

  • Your logic is inarguable. It’s a tough job, but who else would/could do it as eloquently? Thank you for saving us all from bad science! Fascinating reading, with many important points made.

  • Pingback: I must be psychic (low fat diet "triumph" news reports) | Mark's Daily Apple Health and Fitness Forum page

  • “the carb intake at 30% is way higher than any genuine low carb diet.”

    We see this time after time, a so called low carb diet that is anything but. The same game was played with fats for years. Lumping trans fats in with saturated fats from healthy natural sources to add bias to a study or trial.

    Well done Zoe for another excellent article.

    Kind regards Eddie

    • I agree. Whenever I read studies like this I look for the number of carbs in the diet that are defining as “low carb.” Usually is way more than any low carb diet would recommend. If that is what I do find, I stop reading.

  • Zoe’s criticisms on relative change is right on. But on the paper, I’m partial to waiting for the paper to be peer-reviewed (however limited that is) and published. The BBC and news story will be forgotten tomorrow. Just a thought.

  • 6 days? Even *failed* diets last at least a week.

    Did the Endocrine Society at least require a comment or two regarding the effect of these diets on hormone regulation?

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