The Science of Fat-Loss: Why a Calorie Isn't Always a Calorie

Calorie counting can work, but it’s often based on pseudo-science.

I’ve examined before how people can lose 20+ lbs. of bodyfat — or gain 34 lbs. of lean mass — within four weeks, replete with measurements and photographs, but there is still a chorus: “That’s impossible! You’d need to have a 4,000-calorie daily deficit” or “That’s impossible! You’d need to consume 20,000 calories per day!”

Nonsense. Thermodynamics isn’t so simple, and you can accelerate your body optimization results by understanding the real science…

I’ve invited Dr. Michael Eades, one of my favorite bariatric (obesity treatment) doctors in the US and the first to introduce insulin resistance to the mainstream, to explain the facts vs. disinformation. He is author of one of the few research-driven weight-loss books I recommend, Protein Power.

Take it away, Dr. Eades…

Dr. Eades:

I’ve taken some heat for my writing that weight loss or weight gain involves more than a simple accounting for calories.

The entirety of mainstream medicine and nutrition believe that calories are the only thing that counts and that a low-carb diet is nothing more than a clever way to get people to cut calories. Weight loss on low-carb diets, so they say, occurs only because subjects following low-carb diets reduce their caloric intake. A calorie is a calorie is a calorie they say. But is it?

I could argue that this idea isn’t necessarily true because of a number of recent studies that have shown that subjects following low-carb diets actually lose more weight than their counterparts on low-fat, high-carb diets despite the fact that the low-carbers consumed considerably more calories. But instead of going through these modern day studies, let’s go back and look at a couple of earlier famous studies to see what we can learn.


In 1944 Ancel Keys, Ph.D., decided to undertake a long-term study of starvation. It was apparent that WWII was going to be over soon and that much of Europe was starving. Although word of the mass starvation in concentration camps was just starting to filter out into the world, it was well known the Europeans, especially Eastern European, were not getting enough food. Keys wanted to do a study of starvation to see what really happened during the process so that at war’s end the victors would have a better idea of how to deal with the starving masses they were sure to encounter.

Key’s recruited 36 young male volunteers from the cadre of the conscientious objectors. These were healthy, normal weight men, most of whom were working for the Civilian Public Service (CPS), an entity created to provide jobs of national importance for conscientious objectors. The men responded to brochures and bulletins distributed in the various CPS barracks showing a photo of three French toddlers staring at empty bowls over the question: WILL YOU STARVE SO THAT THEY WILL BE BETTER FED?

The subjects came to the University of Minnesota where they were housed in the cavernous area underneath the football stadium for the course of the study. They were basically kept under lock and key for the study so that Keys and his colleagues could ensure compliance. At the start of the experiment the men were fed sumptuously for the first 12 weeks.

A full-time cook, two assistants and a dietitian monitored the food intake to the smallest fraction. According to The Great Starvation Experiment**, an excellent book about this famous study, during this lead-in phase the men ate well. A typical days food would include

a typical lunch… [that] consisted of fricasseed lamb with gravy, peas, and a carrot and raisin salad. For dinner…the men ate roast beef with gravy, whipped potatoes, tomato salad, and ice cream for dessert.

Although the three meals per day the men received added up to around 3,200 calories, which they were told approximated the normal American diet, the men said that they had never eaten better in their lives.

On day one of the starvation portion of the study, February 12, 1945, the rations were cut substantially.

The group shifted overnight from the three relatively generous meals of the control period to only two Spartan meals per day, a breakfast at 8:30 AM and supper at 5:00 PM.

The meals were designed to approximate the food available in European famine areas, with a heavy emphasis on potatoes, cabbage, and whole wheat bread. Meat was provided in quantities so small that most men would swear in later years that none was included at all.

One of the three dinners included the following:


185 grams of bean-and pea soup (made with 5 grams dried peas, 16 grams of dried beans, and 15 grams fresh ham)

255 grams macaroni and cheese (made with 130 grams wet macaroni, 12 grams lard, 108 grams skim milk, 2 grams flour, and 35 grams American cheese)

40 grams rutabagas

100 grams steamed potatoes

100 grams lettuce salad (80 grams lettuce, 10 grams vinegar, 10 grams sugar)

The relatively bulky 255 grams of macaroni made that particular meal an anticipated favorite among the volunteers. The wet macaroni served was roughly the amount required to fill a coffee mug about three-quarters full.

Over the twenty-four week starvation part of the study, the subjects not only lost a considerable percentage of their body weights, but suffered a number of problems as well. As the time wore on the men thought ceaselessly about food, they became lethargic, they were cold all the time, they became depressed, they developed bleeding disorders, their ankles became edematous, and some developed more serious psychological disorders.

Below is a photo of one of the young men in this study (the book shows multiple photographs – this one is typical of all the subjects). The first photo was taken a couple of years prior to the start of the study, the second is with about a month shy of the end of the experiment.


This young man suffered such psychological turmoil from the semi-starvation that he chopped off several fingers of his left hand a month or so after the bottom picture was taken.

The men in this study consumed macronutrients in the following amounts daily: protein 100 gm, fat 30 gm, and carbohydrate 225 gm. If you express these intakes as percentages, you come up with 25.5% protein, 17.2% fat and 57.3% carbohydrate.

Average energy intake of the subjects in the experiment: 1570 calories per day.

Now let’s look at another experiment conducted about 25 years later.


In the late 1960s John Yudkin’s group at the University of London performed a study that is most interesting in view of the Keys’ semi-starvation study. (Click here to get the complete pdf of this study)

For about 15 years Dr. Yudkin and his team had been running a weight loss clinic out of the university hospital using a low-carb dietary approach. Despite the patients’ doing well on the program, he and his staff had received the same criticisms all of us have who treat obese patients by restricting carbohydrates. In addition, because of his academic standing and long list of scientific publications, Yudkin’s peers had given him heat over the fact that his diet didn’t provide enough of all the vitamins and minerals required for health. As a consequence, he decided to do a study to see if there was any substance to their fault-finding.

He recruited 11 subjects aged 21-51 years for his study. He and his staff evaluated the regular diets of these 11 subjects over a two week period. The volunteers were then instructed on the basics of low-carb dieting as it was done in the hospital clinic and followed for two weeks on this regimen. The goal of the study was to determine the dietary intake of the essential nutrients in the low-carb diet to see if there were inadequacies.

Here were the low-carb instructions:

The instructions relating to the low carbohydrate diet were identical to those given to patients attending a hospital overweight clinic under our supervision. Essentially, the subjects were asked to take between 10 and 20 oz milk daily (about 300-600 ml), and as much meat, fish, eggs, cheese, butter, margarine, cream and leafy vegetables as they wished. The amount of carbohydrate in other food was listed in “units” with each unit consisting of 5 g carbohydrate; the subjects were told to limit these foods to not more than 10 units (or 50 g) carbohydrate daily.

As the low-carb portion of the study was progressing, Yudkin and his staff evaluated not only the intake of these subjects, but their mental status as well.

In conformity with our experience with this diet during the last 15 years, none of our subjects complained of hunger or any other ill effects; on the other hand, several volunteered statements to the effect that they had increased feeling of well-being and decreased lassitude. The average intake of calories and of protein, fat, and carbohydrate for the 11 subjects…were remarkably similar to those obtained for the six subjects of the previous study. [Yudkin had published a study in The Lancet in 1960 looking at the caloric and macronutrient intake of subjects on low-carb diets.]

Here is the chart from Yudkin’s paper showing the caloric and macronutrient changes when the subjects shifted from their regular diet to the low-carbohydrate diet.


The macronutrient consumption was 83 grams of protein, 105 grams of fat and 67 grams of carbohydrate. Putting this into percentages of overall intake, we find that diet was 21.3% protein, 60.6% fat and 17.1% carbohydrate. The energy intake was 1560 calories per day, almost exactly the same as the Keys study described above.

And, remember, these people were given all the food they wanted to eat. They weren’t forced to drop their calories to 1560 per day – they did it spontaneously because they had eaten until sated.

Here is the data in tabular form.


As you can see, the big difference is in the carbohydrate intake and fat intake. They are just about the reverse of one another in the two studies.

Both studies provided between 1500 and 1600 kcal per day, but with huge differences in outcome. In the Key’s semi-starvation study (high-carb, low-fat) the subjects starved and obsessed on food constantly. In the Yudkin study (low-carb, high-fat), the subjects, who had no restriction on the amount of food they ate, volitionally consumed the same number of calories that the semi-starvation group did, yet reported that they had “an increases feeling of well-being.” Instead of lethargy and depression reported by the Keys subjects on their low-fat, high-carb 1570 calories, those on the same number of low-carb, high-fat calories experienced “decreased lassitude.”

Both groups of subjects were consuming the same number of calories, but one group starved while the other did just fine. One group had to be locked down to ensure they didn’t eat more than their alloted 1570 calories; the other group voluntarily dropped their intake to 1560 calories and felt great. What was the difference? Subjects in both groups ate the same number of calories.

Maybe, just maybe it’s not the number of calories that makes the difference, but the composition of the calories instead.

I know that I’m not truly comparing apples to apples with the Keys and the Yudkin studies. But the Yudkin study does confirm Yudkin’s 15 years of experience before he wrote his paper and they confirm my 20 plus years of experience taking care of patients on low-carb diets. I’ve had many, many patients who have stayed on low-carb diets for much, much longer than the men in Keys’ experiment stayed on their diets of roughly the same number of calories. Most of the papers in the medical literature on low-carb diets show a spontaneous drop in caloric intake that’s about what Yudkin documented when people switch over to low-carb diets. It stands to reason that if someone had replicated Keys’ experiment using the same number of calories, but with much more fat and a lot less carbohydrate, that the outcome would have been much different.

Yet the calories would have been the same.

So, I’ll say it again. It’s not simply a matter of calories, and anyone who says it is should perhaps give the issue a little more thought.

** Gary Taubes’ book Good Calories, Bad Calories devotes a couple of pages to this semi-starvation study as well.

Enter Tim: This is just one of several topics I’d like to explore within the real-world science of body redesign — anything in particular you’d like to hear about?


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251 Replies to “The Science of Fat-Loss: Why a Calorie Isn't Always a Calorie”

  1. “Maybe, just maybe it’s not the number of calories that makes the difference, but the composition of the calories instead.”

    Well, energy is energy. Presumably what is meant is “but the composition of the source of the calories instead”.

  2. Yudkin’s diet was followed (by 8 women and 3 men — seems a strange makeup; why not go for 50:50?) for only 2 weeks. There is no mention of weight — would the participants have ended up looking semi-skeletal in the long run, as in the other study, despite feeling well?

  3. What is the perfect daily consumption of food in order to get all the amino acids, nutrients and micronutrients and water and fat to absorb those nutrients in recommended dosages? I believe someone I read (perhaps Tim) suggested that being able to consume them all on daily basis would mean massively overeating. Whether that is true or not, if someone were to attempt such a thing, and sought to balance this massive calorie diet out with a rigorous Michael Phelps style swimming routine plus sauna+steam room and cold therapy and whatever else needed to burn calories, release fat and toxins and sweat out toxins out of the bloodstream and so on… What would the “perfect” diet look like? (Supposing such a thing can be defined).

  4. Did the Yudkin example have all men or both male and female. The Keys study only had men, as it sounds. Males and females require different caloric intakes so this could make quite a difference.

  5. I have to tell you that I have a friend who have tried both diets (high carb, low fat) and (low carb, high fat). He told me that the high fat diet made him lose weight much faster than the high carb diet, but not as easy. He would get cravings all the time with the high fat diet, he was very exhausted all the time, he told me that he would wake up in the morning feeling like he was just running in a marathon. And it really made him so tired, nervous and angry all the time. While the high carb diet may be slower in fat burning, at least it is more sustainable and realistic. As for me, I don’t recommend either, my diet would be rich in protein, complex non refined carbs and healthy fat. No elimination or significant decrease in any of the three macronutrients, as the three is needed for a fully functional body.

  6. Hi Tim,

    I have been on diets my whole life, crazy bad metabolism, started eating low carb in the early 2000’s but always cheated. I was recently given a the diet “eat to live” by Dr. Dan Furmahn and I like it. He was featured in the documentary film, “Fat , sick, and Nearly Dead.” I Lost 30 pounds at the beginning of the year on the 6 week plan and have kept it off. But I only loose on the six week plan. The benefits I have noticed are, major mental clarity, lighter feeling in my body and intestines, and no bad cravings. I eat as much as I want so no deprivation just elimination of foods. I was really surprised that it works I was a dedicated hi-pro girl check it out.

  7. Thanks Tim, love posts like this.

    Although I do not religiously follow the 4hr body diet, I have added protein to every meal, and upped my good fats such as avocado, and since doing this I have reduced my comfortable & constant weight by 7llbs. This is pretty amazing considering I haven’t made many other changes, and it’s been no additional effort, 112lbs from 119lbs!

    I didn’t believe the scales when I saw them and tested my weight on different scales to make sure!

    It’s nice to get to 35 and be surprised by how best your body works.


  8. Perhaps this is too narrow a topic, but certainly relevant to body redesign. After having lost 175 pounds over the last ten years (with plenty of ups and downs), I would like to get educated on the subject of skin removal surgery. Internet searches are just too polluted by advertising to yield comprehensive and objective information.

  9. Tim about safety of low carb diet on long term? My hipotesis is that its safe. But Im hearing there are no studies on long term.

  10. Yudkin did not lock down his subjects, which means that most likely they were eating more calories than they claimed. I agree that calories in vs calories out mentality has major flaws, but I don’t think we can compare these 2 studies when we don’t really know the exact calorie intake. People are notoriously bad about keeping track of calories and macros in what they eat.

  11. Tim, Dr Eades, I’m a fit 54 and I’ve followed a ketogenic diet for a 2.5 years (on and off) with great results (body comp, blood) which i have monitored carefully. A couple of questions interest me at the moment: (1) Dietary fiber. I haven’t found much in the keto literature addressing fiber requirements. A decade ago most people were saying you should aim for 30-40 g of fiber a day. But it’s virtually impossible to get this if your carb intake is < 50 g / day. I get some fiber from nuts and berries but decided to supplement with a tablespoon of pysllium husk daily (which doesn't add to carbs or calories because its not digested). Even so, I'm still far from 40 g/ day of fiber. What is the latest thinking about dietary fiber and do you have any suggestions about how to get adequate fiber on a low carb diet? (2) Since starting the keto diet 2 years ago my blood glucose and insulin have been at low levels, as expected. (last lab test was 66 mg/dl fasting glucose; HbA1c was 5.1% and insulin 2.3 ml/U/L. My daily blood tests done at home consistently show glucose around 80-85). However, over the same period i have also noticed an increase in SHBG (146 nmol/L latest) (an inverse correlation with insulin and SBHG has been reported in the literature) and a drop in free testosterone (latest 2.57 ng/dL), total T (657 ng/dL; was 890, 5 years ago) and a corresponding impact on libido. These things may or may not be causally related to the diet but I'd be curious to know if you have observed this effect elsewhere, or if others have reported it.

  12. I don’t get it: Why did subjets in the starvation experiment get skinny on a high carb diet while carbs are not recommended because we get fat?

    1. Because there were way too little calories to keep their bodies up and running. If you starve yourself, in any way, you will lose weight.

  13. Genetics also heavily influences what type of diet best suits an individual for weight loss or ideal body weight maintenance. Weight loss isnt a one spproach fits all – hence the many diets that exist. Whole natural foods, balanced meals that contain protein fat and complex carbs (found in their most natural unprocessed state) will nourish the body and mind – so physically and psychologically one isnt being deprived and over time this will produce the most sustained results. The body and ones appetite will self regulate to obtain snd maintain ideal body weight. I hope 🙂

  14. Great post,

    This is preaching to the choir but it’s amazing to think how much less controversial this idea is than it was 10 years ago when Gary Taubes first brought it back. I’m an entrepreneur and physician that runs the largest low carb weight loss registry in the world with 3,800 members from 71 countries. The stories from around the world are really inspiring. I just recently gave Grand Rounds at Inova Fairfax Hospital on this exact topic. You can see the talk here. It had the longest Q&A session ever I’m told.

  15. I’m missing some information about the studies here.

    First of all, it seems that in the low-fat study, the participants started out with a healthy weight. The second study, as well as the experience of the author, includes mostly or only overweight people. Overweight people have, in a survival situation, much more reserves to get energy from. This is how they lose weight.

    Overweight people that lose weigh usually feel fine, however they drop the weight. People with a healthy weight that really starve themselves, on any crash diet, usually feel cranky.

    In addition, I would like to see the intake (number of calories) compared to the work the participants in the studies had to do.

    As you guys said yourself: it is NOT that simple. Losing weight and diets are way more complex than just counting calories.

  16. Feel free to use me as your human guinea pig. I used to weigh 180lbs and I was quite athletic. I now weigh 275 lbs and work a very physically demanding job but only gain… I am obviously eating lots of carbs. It’s more mental than people realize…

  17. Hello… The Yudkin Study did not lock the participants up. How can you make sure they adhered to the diet and did not eat any Carbs? You can not verify that which makes the study less accurate than what this post suggests.

  18. Every time I read about Keys’ study on starvation and see that the participants got 1500+ calories, I think, “buncha whiners!” Anyone else on here ever go on Weight Watchers back in the ’80s? WOMEN’S portions were about 1100. On this, most of us were young women with houses to run, kids to deal with, maybe an outside job, etc. We’d prepare our own food, often independent of what we cooked for our families, we’d deal with celebrations and other food temptations, we’d add exercise (Pep Step), etc. No one I know ever performed self-mutilation either.

  19. What about optimizing physical performance while acheiving body composition improvements? I feel like sure, lower carb diets can definitely be more effective in weight loss, but what happens to athletic performance as a result

  20. This analysis completely ignores that the men in the earlier study were doing this as an extension of some humanitarian outreach. As the article says, they were contentious objectors who responded to a call that said “WILL YOU STARVE SO THAT THEY WILL BE BETTER FED?” then they were held in isolation for several months. That is not similar to being observed and then told you can eat as much as you want except low carbs…Love your stuff, Tim but this is not really proof of anything.

  21. Just a quick note:

    One study has a supervised portion control

    the Other study has “instruction how to”, without the same control.

    try randomizing people into two groups, each with a different protocol in the same setting.

    Then you may be able to compare the two approaches.