Sugar vs fat on BBC: which is worse?

Sugar or fat, which is worse? That’s the question in the BBC documentary “Sugar vs. Fat” that aired the other night. And it’s been a long time since I got so many e-mails asking me for comments!

It’s an interesting setup. Two identical twin brothers – both of them doctors – go on a diet for a month. One on an extreme low fat diet, one on an extreme low carb diet (not even vegetables are allowed!). Here’s some background information:

MailOnline: One twin gave up sugar, the other gave up fat. Their experiment could change YOUR life

You can watch the show online here.

Unfortunately they end up mostly “confirming” their preconceived ideas. Ready? Here comes the spoilers:


Obviously when there is only one person on each diet, chance plays a big role. But I think the findings were more or less what could be expected, it’s mostly the ignorant (or TV-drama) explanations I have objections to.


First thing first. Even though both brothers were at a fairly decent weight to start with, the low-carb brother lost the most weight: 4 kg (9 pounds) vs only 1 kg (2 pounds) for the low-fat brother.

As study after study show more effective weight loss on a low-carb diet, this should be no surprise. The loss of fat was 1,5 kg on low-carb (a good result in a month) and 0,5 kg on low-fat. Most of the rest was probably fluid. On a very strict low-carb diet you quickly lose a kilo or two of glycogen and water weight.

How much – if any – muscle mass the participants lost is impossible to know as the BodPod test only measures fat mass vs. non-fat mass (including water).

Brain function

For testing the brain function of the brothers the producers chose to make them do stock trading with fake money.

This shows that the producer is ignorant or just interested in a dramatic show. Why? Because short-term stock trading – without insider info or other illegal tricks – is a game of pure chance. It’s been convincingly shown that a trained monkey has a 50% chance of beating a well-educated stock broker. Why? Because it’s all chance.

In other words this test is rubbish, but the low-fat brother wins.

More interesting and relevant is that the low-carb brother complains of feeling “thick-headed”. I’m sure he’s honest. Going on an extreme low-carb diet – without even vegetables – can absolutely result in problems concentrating etc. for a week or even more, before the body and brain adapts to burning fat and ketones.

This problem can often be partially avoided by increasing the intake of fluid and salt. And after a week or two it’s normally gone.


For testing their exercise capacity the brothers do “long sessions of uphill cycling”. The low-carb brother predictably loses badly.

Why? Two things: the body needs weeks or sometimes even months to adapt to high-intensity exercise, using mostly fat and ketones. And even then you might need a little bit of carbs for explosive and anaerobic sports like this.

I’ve interviewed Dr Peter Attia who successfully races his bicycle for hours on a very low-carb diet. Even he uses a little bit of slow-release starch for maximum performance on his long training sessions:

YouTube: Very Low Carb Performance


Finally the icing on the (diabetes) cake. The doctor claims that the low-carb brother has become “almost” pre-diabetic by eating low-carb! The word “almost” should actually be interpreted as “not”. I wonder if the doctor knows the first thing about low-carb and diabetes. In fact I wonder how much he knows about diabetes at all.

The low-carb brother has a fasting glucose of 5,1 before the diet (normal) and a fasting glucose of 5,9 after the diet (normal). Did you catch the word “normal” twice? Yes, thats right, a fasting glucose of up to 6,0 mmol/L is considered normal, at least in Sweden. It also varies significantly from day to day. If we tested the doctors’s own fasting blood glucose it might be 5,9 today and 5,1 tomorrow.

The result could be due to chance but sometimes the fasting glucose level actually gets slightly higher on an LCHF diet, while the glucose levels during the day (after meals) is way lower. This is probably because the body is adapted to burning fat and so the need for burning glucose when fasting is lower. Thus you don’t get the same fasting “dip” in sugar levels.

They also did glucose tolerance tests – a much more relevant test. But the result of the low-carb brother is never mentioned. I guess it was normal.

The fact that diabetes is effectively treated with a low-carb diet should tell us everything we need to know. You don’t get type 2 diabetes by eating a diet that can cure diabetes. And you certainly don’t get type 2 diabetes (strongly correlated to obesity) by losing 4 kilos of excess weight in a month.


The documentary concludes that it’s not about fat or sugar, it’s about avoiding processed food with both fat and sugar in it. I’m sure that strategy would work fine for these two fairly fit brothers. It’s an excellent start. But it’s not enough for everybody.

In people with obesity and diabetes studies convincingly show that low-carb diets are more effective.

Finally, while a super-strict low-carb diet is not necessary for everyone and has possible side-effects (especially during the first week or two) it certainly do not result in diabetes. That’s just ignorant.

What did you think about the documentary?


Diabetes – How to Normalize Your Blood Sugar

New Study: A Low-Carb Diet and Intermittent Fasting Beneficial for Diabetics!

Football Champions on a Low-Carb Diet

Swedish Expert Committee: A Low-Carb Diet Most Effective for Weight Loss

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  1. Allen
    Thank you so much for having the smarts to question many items in this story. I have every other "news" organization fall for this hook-line-and-sinker with no questions whatsoever.

    First, these two, if they even did these diets that they said they did, only did them for a month. They must have worked hard at it too because one lost "2 pounds." Just because of water weight, your weight can change 4 - 5 pounds any day and it means nothing.

    Next, I am on a low-carb diet, and with the possible exception of the first two weeks, I've never had a lack of energy. Just the opposite actually. And my blood sugar certainly hasn't gone up, its gone way down, just like my triglycerides. In fact the only thing going up was my HDL cholesterol.

    Why do news organizations carry such fake stories like this? Its sad, actually.

  2. royal
    To answer your question Allen- WHY DO.....
    Because the world now "runs" on lies, deceit, misinformation and scams- - This "study" is no different. For full info see EDWARD BERNAYS
  3. Mark
    It's rather imporant to know exactly WHAT is involved.
    70g of fructose, galactose or galactan is 0g of glucose
    70g of sucrose or lactose is 36.8g of glucose.
    70g of glucose is 70g of glucose.
    70g of maltose is 73.5g of glucose.
    70g of maltodextrins is somewhere between 73.5g and 77.8g of glucose.
    70g of amylose or amylopectin is 77.8g of glucose.

    Thus 70g of "carbs" dosn't really have much meaning. (Nor does 70g of "sugars" for that matter.)

  4. Mark
    How did the idea that plant fats completly unlike those found in mammals were "healthy" to eat ever get started in the first place?
    Since it's an extraordinary claim where's the extraordinary evidence?
  5. 1 comment removed
  6. Matias MOnsalves
    I think these Documentary wast that good, the LCHF was leto adapted? i don't thing so, and also what organism after 10 month with suppression of a macronutrient doest get a overcompensatory response as it was on the glucose tolerance test?...No 24 hour response on these marker.
  7. LIza
    I watched this on demand recently and can only begin to describe my general outrage in the design of this experiment.

    I wrote a rather lengthy email to a colleague who asked me if I'd watche it, and it ran in the same lines as the doc's comments above.

    Personally I find Sam Feltham's self monitored and conducted experiments all the more accurate and well executed.

    BBC, keep trying.

  8. Jonny
    Fresh fruit and veg are the way to go. We're not supposed to eat meat and dairy. Besides weight-loss (BTW you won't be fat if you sustain a fruit and veg diet, fact), you need to consider other factors such as illness - namely diabetes and cancer. Eating a diet high in meat and dairy is being linked to increasing cancer rates.
    Reply: #109
  9. Zepp
    Strange.. becuse its about ones bodys capability to handel glucose!

    But if you have done any new sciens about it, we gonna meet in Stockholm when you get your Nobel prise in medecine!

    Then we can take a coffe and talk about your new sciens!

    Reply: #110
  10. Jonny
    No new science, just nature and common sense and current science.
    If you were designed to eat meat you would lick your lips when you saw a little dog walking by, or when you see road-kill. Also, your teeth and jaw shape would be different and you would likely have claws rather than fingernails! You certainly wouldn't need to cook the meat either, as nature would have given you a gut that could handle the digestion of raw meat!

    Also, name me another animal that consumes the milk of another animal? Surely humans have not been designed in such a way that unless we artificially impregnate a cow, steal its calf, and then hook the cow up to a milking machine all day, we will miss out on vital nutrients!!??

    Stop believing the rubbish that is out there, and start thinking. Simple really, no Nobel Prize required, thanks

    Reply: #111
  11. Zepp
    Well I can only think about cats, dogs, pigs that drink/eat other animals milk!

    But is you aware of the name Mammal?

    It means milk drinkers!

    We are born milk drinkers.. other Mammals too.

    Do you think snakes or sharks have claws.. read your biology book again!

    You do have an odd perspective to biology.

    And I can tell that Homo Sapiens is the only creature that adapted to coocked food.. we are in moste circumstances relayant to that.

    We are omnivores,, if you like it or not,, we can live on a lot of food substances.. and be healty!

    But to day.. its a problem of to much glycemic load thats moste problem.. one have to use them.. there are a shortige of storage facilitys in our body.

    We vill see each other when you get the Nobel prise in Stockholm.. then I would listen to you!

    Reply: #112
  12. Jonny
    Hehe, you are funny. You must have strange mammals where you live! I've never seen a mammal (in natural habitat) drink the milk of another species. Of course mammals drink their mother's milk as babies, but once they can eat solids the nursing ends. I've never seen a pig, cat, dog milk a cow! Cow's milk is designed to provide the nutrients needed by a calf, not an adult human!

    Are you sure we are omnivores? Name me another natural omnivore? Then check the teeth and jaw of your chosen animal. How similar is it to human teeth and jaw?

    Finally, how can a digestive system develop naturally where the food needs artificial preparation? Are you saying that cells have a naturally programmed knowledge of the effects of cooking otherwise inedible food?

    So what is more realistic, the premise that humans were designed to eat only foods which we can naturally digest in its raw state (fruit and vegetable), or that humans were designed to cook to get their natural diet? Sometimes you need to follow logic and look around you.

    Reply: #113
  13. Jenny
    Omnivores: all kinds of pig, all kinds of birds, all but one species of ape/mokey which I don't remeber the name of.
    Dogs and cats (carnivores) are known to sometime chew grass and flowers and berries.
    There are horses (herbavores) that eats baby birds or fish. (
    And no the aimals are not forced to eat it

    Point me to one herbavore that has the short digestion of a human. likewise we don't have the very short digeston tracks of carnivores.
    We can be poisoned if we eat the wrong kind of herb/vegetable/fruit. In ome cases (like with rots and potatoes) we would get awully sick if we didn't cock them before.
    On the other hand we can eat raw animal food.
    Our teeth and jaws don't look like that of a bird or a pig, nor does it look like a cow or a horse, or a cat or a dog. in fact it barely looks like that of a shimpanse.

    The human developed the ability to cook her food way before we developed agricultur. Therefore we are able to eat a huge variety of foodstuffs, from herbs and rots to animal products of different kind.

    We are supposed to eat nutrient and calorie dense food. Not half our weiht in greens each day. Or maybe you have the trunk size of a monkey? Or four stomaches like a cow? Or the need to throw it up and chew your food again?

  14. shaun
    Humans from evolution were designed to adapt for our diets depending where on earth we are living,as a specie we were not giving a specific diet to eat,our species learned from experience wot we could and could not eat,our jaw structure is different from any other specie as we are unique to evolution,since the first man there is proof we cooked foods and had the ability to digest both meat and plant etc,name me an animal wot can digest the same as a human,mankind is constantly evolving in many ways depending on where we live,we adapt to altitude, pressure ,temperature,oxygen levels,we were given an advanced brain to survive which we used,
    for example the first man would have been very active walking long distances,foresting hunting capturing food and basic surviving would have needed nutrients from both animals and plants berrys nuts etc.back to design of our teeth we have molars for chewing and canines for biting tearing of flesh ?,wot part of eating fruit and veg would we need canines for?
  15. Luke
    So low-fat beat low-carb in every respect? No interpretation required. Eat carbs, not fat.
    Reply: #116
  16. Zepp
    Nooee.. low calorie beats every other regime,, as long as you can stick to it.. but thats not long!
  17. Sandy
    I don't care for the fact that "sugar" and "carbs" are used interchangeably in this. For all processed sugars are carbs, not all carbs are processed sugars. The title should really be - "carbs vs. Fat". This does nothing to isolate processes sugar as an identifier to obesity and weight loss difficulty. The body NEEDS carbohydrates to function properly - it's all about which carbs you're ingesting.
  18. Mike
    Wile this is all true that humans are designed to eat fruit & veggie, our jaws/teeth are not designed for rough meat & our digestive system is not strong enough to eat raw meat chicken/beef/pork without geting sick, but.. Our system is stable enough to eat raw fish & sea food. So to add to the theory of human diets design I agree. We where not born/created with the theory of a stove or fire to cook our foods. Also as much as I love milk, I do agree it is liquid food for infants that can not chew or digest substance yet due to a weak digestive system. Grown adults should not drink milk in theory. No adult animals in the world drink milk after they pass the infant stage.
    Also our teeth are not made for tough meat, not many can say they have but have you ever tried to eat raw chicken ham or beef? I have not but I can imagine how impossible it would be with our "crunching teeth" not made for cutting or shredding. Reason we only prefer to eat "tender" meat like filet steak etc. Humans should eat fruit veggie & sea food. These foods have natural sugar, low fat & high protein. Unlike red meat wich is full of fat. Or chicken full of disease us humans can not eat without cooking.
  19. Galina L.
    Humans have not only teeth, but brains and hands. Pounding and cutting in pieces can make meat easy to eat even without cooking. There are dishes made with raw meat in almost every culture.
  20. shuaib
    This is very interested
  21. shuaibu muhammad Dan-kano
    I really enjoyed the show.....
  22. fats/weight solution
    I need someone who will educated me more on fats/weight reduction because am a little bit fat than last two months +2348180255262 and my E-mail thanks and
    Reply: #123
  23. Zepp
    Try this.. its not perfect.. but a good try to explain what its all about!

  24. Roger the eater of Gods gifts
    Eat Drink and be Merry, in Moderation.

    Good Luck ! and Enjoy!

    Don't Worry be Happy!

  25. teak
    to the user to mention the Paleo diet, if you look up the actual Paleo diet and the original one you will see it includes numerous amounts of bugs! Is that what you eat? If not it is not even the real Paleo diet. I find it strange also how so many people still do not realize that vegetables them self contain more than enough protein without absolutely any chemicals carcinogens and a slew of other crap.There is not one single benefit from eating meat or any animal products whatsoever. Not one. People often ask or say ...oh my god you don't eat meat how do you get protein? And I tell them the same way our strongest mammals on the planet do! With a plant based diet. I said based....which does not mean I do not enjoy the occasional treats of sweets or anything else.. my opinion all of this is simple common sense. One ingredient Whole Foods. Lose the dead animal flesh and the other dairy crap that was meant to make a baby cow into a 2500 pound heifer!
  26. Van
    Agreed, it was eye-wateringly poor as far as being a well-designed and fair comparison goes. It's difficult to imagine how it could have been more poorly conducted.

    - Very likely the "high fat" diet was also far too high in protein. Certainly not a "well-formulated" high fat diet.
    - Test subjects were not overweight, indicating that genetically they fall towards the "carbohydrate tolerant" range of the population and therefore have less to benefit than most from switching to high fat
    - Adaptation time for high fat very short
    - Mental test was a crapshoot
    - Physical test was far too anaerobic, playing to all the strengths of high carb
    - Ignorance about diabetes (higher fasting glucose, if anything, is strongly implicating protein toxicity)

  27. Caeleigh
    So I guess they can eat 250 calories worth of Oreo cookies and that's JUST the same as 250 calories of meat and veggies. WELL, HELL, I'M SOLD! Sign me up!!!!
  28. Bruce G
    This show proved essentially nothing.
    A month is too short a time for chronic change.
    And I agree with others above who say the test should have been a crossover with a washout period. I'd add that each diet should have been maintained for 12 months.

    But this would have highlighted the stupidity of the test as neither brother would have tolerated either diet for that long due to the extremity of each.

    It would have been more meaningful to make the macro ratios similar to the dietary habits of real people, rather than ridiculous extremes that essentially no one would follow.

    The pro Paleo conclusions reached by dietdoctor and those in the comments above, totally ignore the most powerful dietary studies done to date (Adventist Health Studies 1 and 2), which show unequivocally plant based eating trumps every other form of diet re the major causes of death in Western society. The low carb Paleo crowd have several generations of prospective study to go before their faith carries any punch.

  29. John

    All I will say is you need to do some more reading. I know how I lost weight, and how I reversed type 2 diabetes, and it wasn't by steering clear of fats and protein. Your Adventist Health can go begging as far as I am concerned. I know on which side my wheat and sugar-free bread is heavily buttered.

  30. Loretta
    I know what is working for me and I've been on every diet that has come out since I was 12, 37 years ago. I tried the low fat, high carb diet prescribed by the diabetic nutritionist when I was first diagnosed at 35. I've gone from one pill to control my diabetes to using two types of insulin now. Until a month ago, my BGLs wouldn't come down out of the 200s no matter what I did. Now, I am on a LCHF diet and my BGLs have come down to the low 100s. Would I go back to a HCLF diet again? No way! The results I am seeing have convinced me that I will never over-eat on carbs again. I only eat vegetables, meat/eggs/fish, some dairy and lots of fats (coconut oil, butter, bacon grease, avocados, and high fat dairies) and keep my carb content below 20 grams every day. My body aches are almost completely gone too. I feel like a new person.
  31. Anne
    I think it shows that I should rather choose a snack/drink with fat in it, than one with sugar. And that has always been my intuition. Sugar is the criminal ladies!
  32. Sifu Dan
    How about we just control our calorie intake and follow a balanced diet?

    And here's the kicker - EXERCISE!

    The problem with advocating 'fad diets' and cutting out major food groups like carbs, is that you're pigeon holing every single person on the planet into the same diet plan. There is no perfect diet plan that applies to everyone.

    In my travels around the world I have seen how different cultures eat and live. Generally those in Europe have a small breakfast (if any), moderate lunch, and moderate dinner. In Britain, Australia, USA - the tendency is to eat large meals at least 3 times a day.

    Overeating is making people fat and leading to an early death. Not fat and sugar exclusively, but a combination of both in excess.

    #science #dontfollowfads #getinformed

  33. Charles Uibel
    so, a cheeseburger and a coke = sugar+fat?
  34. Debi
    Would have loved to have seen the video. It was "Not Available" on either link.
    Reply: #135
  35. Peter Biörck Team Diet Doctor
    Hi Debi!

    I think this link could work:

    Would have loved to have seen the video. It was "Not Available" on either link.

  36. 1 comment removed
  37. Tazx
    I find the documentary interesting and well made. I think it misses the diference between refined sugar and other carbohidrades, IMHO they are not processed in our bodies in the same way. I also think that the combination of nutrients in one intake is important.
    For the rest, the conclusion, as I see it, is that we should stop thinking of [crazy] diets and turn to eating habits. And essentialy not eating more than our bodies need and doing some exercise. And that's it.
    Nowadays we have easy access to food and we also can get a huge variety of it. If we educate ourselves and learn to appreciate and enjoy every type of food we have it easier to adapt our habits and quantities.
    Cooking your own meals it's also very good for not getting overweight and eating yummy and healthy.
  38. Brad.
    Just watched the video and read all the interesting thought on the posts - What did the Inuit people eat?

    Fat, with some protein...not a lot of fruit and vegetables in the frozen tundra. They all survived really well until stores started to show up.

    The documentary was very single sided with not a lot of forward thinking or time involved doing the tests.

    The scariest movie I have recently watched was "That Sugar Movie" talk about ill effects of!

  39. Karen
    I turned this program off as soon as I saw that they were measuring brainpower by Stockmarket trades! Great to find a good summary of the so-called 'findings' online.
    Reply: #141
  40. Jim
    As a personal trainer and current kinesiology student i have not only seen the outcomes of a healthy diet but tested and personally experienced the effects of different diets. First of all we can start off buy saying your body can not tell the difference between carbs from a chocolate bar or carbs from whole wheat the basic ratios for your macro nutrients are a follows:
    9 calories per gram of fat
    4 calories per gram of carbs
    4 calories per gram of protein
    no matter where they come from your body can not tell. As long as you are eating the correct amount of calories you can lose weight or gain weight eating literally anything you want. Where healthy foods come in is your body composition or how you look. Eating lower amounts of calories will make the numbers on the scale go down yes, but you will not appear or feel fit or healthy unless you eat the proper foods. Your diet should consist of these ratios:
    30-50% carbs
    25-35% HEALTHY fats
    25-35% (approx 0.8-1 gram per pound of body weight) protein
    Carbs are pinned as a criminal as they are known the make you fat and burn off before your fat burns making them seem like just another roadblock in between you and your never ending road to weight loss. It is true they do add fat but they are essential for your diet as they are your main source of energy. Body builders cut carbs during their final days before a competition and feel terrible, weak, lazy, and tired as they have no energy provided from the carbs. a low/no carb diet is harmful for you and should not be taken up without consulting a doctor or nutritionist. Finally i would like to talk about "low fat" and "all natural" foods. All natural foods are in a category with next to no regulations when you eat something that says it is all natural but is packaged and sitting in a grocery store isle you are loading yourself with more chemicals and garbage than if you ate regular regulated non natural foods. Low fat foods are another misconception as many people dive in to low fat foods as they read the nutrition labels and see there is low or no fat, what they dont see is the sugar levels significantly rising. Sugar is stored in the body as fat, more slowly then fat itself but stored all the same. I can not exactly tell you the ratio of sugar to fat but it seems as though 2 grams of sugar equate to 1 gram of fat. most low fat or fat free selections have more than 2 times the sugar levels causing it to be more harm then good. Most adds and diets are scams and false stick to a healthy diet and daily exercise and you will fel and look better with lot of care and dedication you can stop and even reverse the effects of diabetes (although never curing it).
  41. Pino Rossi
    Very BBC. Pretending to be always on the right side of things, while secretly supporting financial capitalism.
  42. Andy
    Is it really a mystery on how to eat to maximize your health and avoid health problems? Sheesh! Eat whole foods, eat mostly a plant based diet, no refined foods, no sugar, cut back on the meat and dairy, and eat less overall.

    This has been proven to maximize longevity and avoid disease time and time again. Yet, everyone wants a magic formula, or pill. Everyone wants to be told that it's okay to eat hamburgers, and ice cream, downed with a lager as long as you do it in moderation. It's not okay. That stuff is toxic for you. We are not evolved to eat it.

    There's a trade-off between maximizing your health, and maximizing your pleasure. Maybe it's not worth living to a hundred years old if you are stuck eating nothing but kale and almond milk.

    But sadly you can't have your cake and eat it too. You have to make a choice but stop looking for the magic elixir.

    Reply: #143
  43. Romka
    Arnold Ehret said it 100 years ago!
  44. 1 comment removed
  45. Gentiann
    Everything in moderation works only for healthy young people...... If it works for you, great! Unfortunately, it's not working for most of us with health issues.
  46. haig
    These twin brothers did a documentary series called "Medicine Men Go Wild" in 2008 six years prior to this "Sugar vs Fat" bbc documentary. In one of those episodes they traveled to a Siberian village where the natives there ate only fish and blubber. For the duration of their stay one of the twins ate like the natives while the other ate a modern western diet with imported foods high in sugars and carbs (eg. breads & jams) from the local convenience store (which most villagers avoid). The results, and their conclusions, were the opposite of what they presented in "Sugar vs Fat"; the brother who ate high fat, zero carb like the villagers reported high energy level, mental clarity, weight loss, and improvements in blood lipids & cholesterol, the other brother on the western diet had negative results across the board.
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