What happens if you eat 5,800 calories of carbohydrate-rich junk food daily?

What happens if you eat 5,800 calories of carbohydrate-rich junk food every day? This is what Sam Feltham is going to find out in a 21-day experiment that he’s now launching. He’ll also monitor various health markers during the experiment.

SmashTheFat: Introduction: The 21 Day 5,000 Calorie CARB Challenge

You may have seen the results of Feltham’s earlier experiment – 5,800 calories of LCHF food daily for 21 days:

What happens if you eat 5,800 calories on an LCHF diet every day?

While eating an enormous amount of LCHF food he didn’t gain 16 lbs (7.5 kg) as simplistic calorie counting would predict. He “only” gained 3 lbs (1.3 kg).

What do you think’ll happen when he consumes 5,800 carbohydrate-rich calories daily over the same length of time?

Contest: Estimate the number of pounds of weight gain for Feltham in the comment section below. Please also speculate on what happens beyond weight gain (tiebreaker in the event of several correct answers). The winner will be honored in a blog post.


  1. Kirk
    This is gonna be GOOD!
  2. Pierre-Louis
    I predict he'll gain around 20 pounds. He will have higher blood cholesterol, higher LDL levels (the bad LDL) he'll also have trouble sleeping, headaches, he's probably going to end up pre-diabetic and he will always be hungry.
  3. Paul C
    He's going to pile on some 21 lbs of mainly fat... and it's going to be visceral fat as well around his liver and pancreas. He may start suffering from Non-Alcoholic Fatty Liver Disease if not end up with Non-Alcoholic SteatoHepatitis (NASH) temporarilly.
  4. Jacqui
    I predict a weight gain of 5kg+
    He'll feel tired and have trouble maintaining energy levels. Headaches, dizziness, short temper and feeling permanently run down.
  5. Adam
    I predict an approx. 26lb gain with an exponential raise in blood pressure. There will also be an increase in lethargy, and you may begin to experience heart palpitations
  6. Logan
    I predict he'll gain 6 lbs. (mostly water weight) and none of his health markers will significantly change more than a few points. (I think it takes a lot more than 21 days for this kind of diet to have a major impact on health)

    Someone has to be the contrarian, might as well be me. :D

  7. charles grashow
    This man is a moron. These "experiments" prove NOTHING.
    Reply: #19
  8. Erin
    I say he will have gained 15 lbs
  9. Paul Allen
    17lbs gain. Some of that will be water/glycogen weight.
  10. Kris
    He will gain about 9-12 lbs and his waist circumference will increase by about 3-4cm.

    Trigs will go up, HDL will go down.

  11. mark
    I predict he will gain 11.5 pounds.


  12. ES
    I'm guessing his BMR is 2800, so I would say 18 pounds of fat stored, plus his glycogen storage will increase 7 to 10 pounds so my final answer will be: 27 pounds in 21 days.
  13. LyndaS
    15 pounds up. His triglycerides will soar and HDL will go down. Hb A1c will rise.
  14. Jennifer Raper
    I predict a 17-pound gain. Other symptoms: rise in cholesterol and blood sugar, lethargy, joint pain. Headaches are also a possibility.
  15. Dyveke Kanth
    I think he will gain 7 kg. Hes body will at first try to get rid of the shit he is eating by throwing up and become sik after eating, when the body adjust to this, his weight will gain. He will get higher bloodpressure, not from salt but from a body in stress, even cortisol levels will go up so as total cholesterol. He will get hartburn and trouble with sleeping, and wondering why he even wanted to go throu this experiment in the first place...
    Reply: #58
  16. kevino
    Depends on his omega6 intake. At a guess (from the pic of 'foods'), maybe 9kg.
  17. Jan
    I know he is probably trying to prove a point. I would prefer that he doesn't partake in this at all. It's not worth it.
  18. natosha
    I would say he probably gain about 18lbs.
  19. Henk
    They prove that he is a moron.
  20. Carbophobic
    I am going to guess 5kg total weight gain. There are too many other possible factors involved so this is just pure guessing.
  21. Jim Fogarty
    While they may not prove anything scientifically they are interesting experiments and I see nothing wrong with challenging the accepted wisdom. As for a follow up to this challenge I would be more interested in seeing what would happen on a high carb low fat calorie reduced diet like the kind so often recommended for weight loss. One rich in "healthy" whole grains and low fat diet foods.
  22. Liv
    I think he will gain 4-5 kg and increase his waist with 4 cm. He will feel more tired and put on more body fat around his belly.
  23. john
    I think he has "hollow legs" so I don't think he'll gain that much weight. I've had times in my life when I've eaten loads and other times when I've not eaten so much, but my body weight stays fairly constant.
    I think he'll get sick of all that junk food though. He normally eats very healthy stuff. I bet he gets spots.
  24. Kindke
    This will just be a repeat of the BBC horizon program why are thin people not fat.

    Its impossible to predict how much fat he will gain because genetics play a large role, he will certainly gain more fat than his LCHF experiment however and his waist will go up 3-4cm. maybe even more,

    BUT the point is, as soon as the experiment ends, the weight will be easily lost and he will effortlessly return to his normal weight. He is obesity resistant.

  25. Jen
    I guess 6.8 kg, mostly water weight.
  26. Nads
    He should have eaten high carbohydrate "healthy" food, to prove a point.
    Reply: #46
  27. Johnnyv
    Hmmm if I wanted to wreck myself as badly as possible with a calorie limit of 5800 per day?
    I guess I would eat sugar, wheat, low protein and omega six rich oxidized fats, approx 50/50 carbs/fat.
    So a donut diet!
    Yeah thats how I would destroy myself in the shortest time possible, however I will not do that because I am not retarded.
  28. Damocles
    4.5kg of fat + 2Kg of water (glycogen stores)

    In the end, this experiment changes quite a lot of variables, and will be criticized on that
    But lets take the resulting weight-gain as an (exemplary) effect of eating too much on a "standard" diet.

  29. Galina L.
    That guy is not a maroon. I guess, with his experiments he is trying to demonstrate how wrong is that popular believe that 3500 excess calories consumption will result in 1 lb of fat gain for everyone.
    My wild guess he will gain 5 lb of fat and 3 lb of muscles as a result.
  30. Lori
    My guess is 12 pounds of spare tire gained, and that he'll feel like a slug and get a lot of plaque on his teeth, but probably not a cavity.
  31. Jennifer B.
    I think he will gain 23.5 lbs. Estimated based on calories plus water weight he will gain from starting up on high carb.
  32. Sean
    This is lame. So he eats real food for one test and fake food for another, why not man up and eat a whole plant based diet and compare it. He'll put on 3.5KG over the 21 days.
  33. Mary A.
    30 Pounds, that is weight gained in 21 days and eating 5,000 Cals. This estimate does not factor in expenditure of Cals. However considering expenditure I would say roughly 18 Pounds give or take.

    What happens after weight gain can be considerable for some but I would say; depression, breathing problems, risk of diabetes ect. But this is speculation for I am not a Dr.

  34. Murray
    I hope he gets liver and pancreas testing during this.
  35. Greensleeves
    I think he'll gain 10-12 pounds; he's naturally a thin guy. His CRP will increase, even double. Waist will expand. Trigs, LDL will also double; HDL will fall. His testosterone will fall. Not a long enough test to ruin his HbA1c. Cortisol will rise. His blood sugar will rise into pre-diabetic levels. Blood pressure will rise slightly maybe 10 points.
  36. Justin B
    So many people seem to be over-thinking this. Its just a simple "calories are not all the same" experiment. That's all. Sam has no malice towards "carbs", as far as I can tell. He seems to normally regard things like sweet potatoes as "safe". Its purely to show that not all calories are created equal. You can just think of this as real food vs junk food. Period. When people still believe that all calories are the same, and that you could do fine eating twinkies all day, as long as you don't overindulge, this is the kind of "common knowledge" that we need to disprove to the public before moving to the more intricate ideas.
  37. Eric Anderson
    The more intersting questions are the delta between an insulin resistant and an insulin sensitive group if any 2) the delta of 80% carbs all complec vs 805 carbs that includes sugar as 25% of calories versus a LCHF 5% Carb (Vegetables as in complex carbs, 15% protein and 80 percent fat (Animal and natural Versus the same LCHF with half of the fats from man made fats like soy, canola, Corn, etcetera.

    Will differences be observed and why have these types of diets not been done?

    NuSi will hopefully be the first of many studies to ask these more fundemental questions about diet, health, biomarkers and real vs not real diet results.


  38. Darcy
    probably about 23 pounds
  39. Hristina S
    I guess he'll put on 2-3 kg of fat and 1-2 kg of water weight. His HDL will be lower, he'll feel very tired, probably depressed, always hungry and bloated, and very irritable. It will take him much more time to lose the fat, than to put it on in the first place, let's say at least 5-6 weeks to do go back to normal body fat percentage.
  40. spareld
    glad i sub to this man his channel is amazing
  41. grinch
    I predict he will gain 7 lbs in the first week because of water weight due to replenished glycogen, but he will say its all fat gain.
    Replies: #42, #47
  42. murray
    "replenished" glycogen? That begs the question. First, what is his state of glycogen going in. Second, "replenish" is an a priori judgment that stuffing glycogen to the maximum the body can stand is a good thing. A fine example of confirmation bias in interpretation. One might as well say someone with a BMI of 35 has "replenished" adipose tissue.
    Reply: #43
  43. grinch
    re·plen·ish [ri-plen-ish] Show IPA
    verb (used with object)
    to make full or complete again, as by supplying what is lacking, used up, etc.: to replenish one's stock of food.
    to supply (a fire, stove, etc.) with fresh fuel.
    to fill again or anew.

    Where did I say anything about whether replenishing is good, and confirmation bias regarding what?

  44. Murray
    " ... by supplying what is lacking" connotes that increasing glycogen to the level the body cannot take any more, possibly due to becoming water-logged and bloated to the point of endangering ion concentrations and increasing blood pressure, is "supplying what is lacking." That is an implicit value judgment that increasing glycogen to the limit of physical tolerance is a good thing. Phinney and Volek (Art and Science of Low Carbohydrate Performance) found the keto adapted cyclists stored about half as much glycogen, that they did not need so much glycogen. It remains to be shown which state of being is better placed on the J-curve of healthy degree of glycogen storage. To imply, without acknowledging there is an issue, that taking the body to the utter maximum of glycogen capacity is replenishing begs the whole question of a good faith investigation into the relative benefits of high-carb and low-carb.
  45. Glen0
    It would be a more worthwhile exercise to consume the 5800 Calories using Carb rich foods that are supposedly good for us like wholegrain bread and cereals. This would help show any difference that is not totally obvious unlike consuming refined carbs which is a no brainer.
  46. commonchild2
    Absolutely agree. Maybe he'll do that as a 3rd experiment next year. He should have gone either 1) low fat with junk or 2) whole food vegetarian but high carb. Why mix in all those 'low fat' foods he purposely pointed out when he was eating all of that other high fat junk food?

    I think he probably has a body that can eat a lot and burn it off easily (the type of people we hate;) but I bet he is also glycogen depleted when started so there will be a lot of water weight gain. Those will cancel each other out and he'll gain 10 lbs.

  47. FrankG

    I predict he will gain 7 lbs in the first week because of water weight due to replenished glycogen, but he will say its all fat gain.

    In the same way the proponents of simple calorie-restriction point to "weight loss" as if it was all fat mass, with no loss of lean muscle tissue?

    This is exactly the point of the exercise... to show up the fallacies of these widely held beliefs.

    Just because you claim to understand that these are fallacies, does not change the fact that the vast majority of the population and health care professionals, still hold them to be true.

  48. samc
    I would predict 5lbs, mostly made up of devils horns on his head. Might have a bit of a tail as well.
  49. Patrick Steil
    I'll guess 22 pounds! :)
  50. Nan
    I predict at least a pound a day, and will do great trauma to his major organs, especially his brain. This is like russian roulette, but with more bullets in the gun.


  51. J
    I'm gonna guess 6#, because I think he has a pretty good working metabolism. If he was overweight and had insulin resistance, he would gain more. In Supersize Me, the guy had abnormal lab values in 30 days of eating fast food. So I think his liver function tests will be elevated, and perhaps his triglyceride level will be up as well.
  52. Martin Levac
    Hm, not easy to make accurate predictions. But based on other similar experiments, I'd say he's going to be very very miserable. He may not gain any weight. He may be one of those who just can't grow fat. He's already lean to begin with. One thing's for sure, his insulin will go up. Depending on his current glycogen status, he might gain weight as water, as glycogen will overflow, requiring more water for this. Now this is an interesting prediction, since it says that the glucose we eat isn't actually spent right way, but instead is stored. But maybe when his glycogen is overflowing, he's gonna have to spend the glucose he eats, right? No, his BG will just go up and up and up. Trigs, HDL, HbA1c, all that stuff, I agree with others' predictions. LDL particle size will shrink. One absolutely accurate prediction is that his blood plasma will become milky and opaque, as opposed to clear while on a LCHF diet. His blood ketones will go so low as to become barely measurable (<0.1mmol). He might get glycosuria. He might even get sick right on the first day. Liver markers will get worse. Heart rate will go up. BP will go up. He'll become addicted to those foods, and suffer withdrawal once the experiment ends. Aches and pains may suddenly appear. He's gonna get tired for no reason. His mood will fluctuate. He'll become irritable. His attention will degrade. His sleep will get worse, he might wake up in the middle of the night with cravings. He'll sweat more. His body temp will fluctuate more. His gut will bloat and he might get digestive problems, diarrhea, constipation. His gut bacteria will change. He may get heart burn and acid reflux. Pasty mouth. Injuries will take longer to heal. He's gonna get more hungry. He's gonna be more thirsty. His eyesight may degrade. Everything LCHF is good for, is gonna get worse for him.
  53. grinch
    According to conventional wisdom, he should gain just as much weight as he did on low carb (after adjusting for water weight changes). Conventional wisdom states that increasing calorie intake above maintenance DOES also increase energy expenditure, but the amount varies from person to person, not so much by macro nutrient composition.

    Also any adverse health effects would also be expected per conventional wisdom and among CICO advocates. The CICO crew would say that these adverse health effects are dose dependent, so as long as you are eating way above maintenance, one should expect adverse health effects of these foods. Twinkie diet guy shows quality doesn't matter that much IF you can keep your calorie intake low.

  54. Peter m.
    I feel sorry for him. He's in such great shape and he'll ruin it lol.
  55. Steve
    The results are in: a gain of 7.1 kg (15.6 pounds) in just three weeks, where on an isocaloric LCHF diet, his gain was 1.3 kg (2.8 pound).
  56. Eric Anderson
    The math seems right ==
    21 days at 5800 calories and a 15.6 pound weight gain is in line with a 3200 per day calorie burn and 2600 excess calories.

    This is in keeping with DOctor Richard K Bernsteins experiance of adding 1000 calories a day to skinny diabetics diets to try to help them gain desired weight. After 6 months no gain.

    Maybe the NuSi diet studies under very controlled conditions will demonstrate to some of the doubters the delta of HFLC and the SAD high carb western diets.

    Funny we do not see the High carb gurus running longer term testing on weight, A1c, Fasting glucose and insulin. Maybe they have and just do not publish? The last 40 years of USA higher carb diets and more illness speaks for itself. Eric

    And no wonder Vegataian have higher A1c and fasting Insulin levels!

  57. greensleeves
    Dyveke Kanth should be the winner; as Sam reported yesterday he gained just over 7 kilo.

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