Low Carb

Why Low Carb Is High in Fat – Not Protein

Too much protein for 1 day?

A lot of protein

Why should a low-carb diet be high in fat, and not high in protein?

I’ve often recommended switching to a diet higher in natural fats and lower in refined carbohydrates. What’s the deal with dietary fat? Simply put, dietary fat does not raise insulin. And hyperinsulinemia is the main driver of obesity. Hyperinsulinemia means literally, high insulin in the blood (hyper means high, and -emia means blood levels).

So, logically, switching refined carbohydrates, which raise insulin significantly, for dietary fat, which does not, can lower insulin levels significantly even if you take the same total number of calories.

But what is so different about dietary fat compared to both protein and carbohydrates that makes this true? It all comes down to the different ways that proteins and fats are metabolized.

newhot2This also illustrates the difference between the insulin hypothesis and the carbohydrate-insulin hypothesis (CIH). The carbohydrate-insulin hypothesis holds that insulin is the main driver of obesity, and that the main driver of insulin is carbohydrates. Therefore, if one simply reduces carbohydrates, insulin is reduced as well.

I think this is not entirely true. Animal protein, for example, is highly insulinogenic (provokes an insulin response), even to the same degree as many refined carbohydrates. If you eat according to this hypothesis, you should be able to eat as much protein as you like without problems. But this is not true.

A nuanced version of CIH

The insulin hypothesis, or the Hormonal Obesity Theory (HOT), is a more complete, nuanced version of the CIH. Insulin is still the main driver of obesity, but there are many different ways that insulin can be raised or lowered.

For example, insulin resistance, fructose, animal proteins, incretins, vinegar, and fiber can all be incorporated into this more complete model of obesity, which still holds insulin at the center of the web.

newhot12In this case dietary protein is not given a free ride, since it stimulates insulin. If you overeat dietary protein, according to the HOT, you can still develop obesity.

This is the key insight behind the more recent LCHF (Low Carb, High Fat) movement rather than the pure Low Carb movements (Atkins and others) which do not restrict either fat or protein.

Fat vs protein and carb metabolism

But there’s a fundamental difference in dietary fat metabolism that differentiates it from proteins and carbs. It has almost no insulin effect. Why not? Because it doesn’t use the liver for metabolism. Insulin is only necessary for burning glucose, not fat.

So, during normal metabolism, the three macronutrients are absorbed and metabolized completely differently. Let’s start with carbohydrates. These are chains of glucose, mostly as amylopectin or amylose. There are different forms of amylopectin (A,B, and C) which are metabolized differently. Amylopectin A is the most easily digestible and the form found in bread. Amylopectin C is the least digestible and is found in beans. The reason beans make you ‘toot’ is because much of the indigestible amylopectin C makes its way into the colon where bacteria ferment them and create gas which comes out the bottom end to the endless amusement of little boys everywhere. Bananas contain amylopectin B, which is intermediate between A and C.

This difference becomes obvious in the glycemic index, which is a good indicator of the insulin effect for carbohydrate foods. The GI for wheat is very high, and for beans, it’s quite low. So, carbs are not equal, and not even amylopectin is equal. It is the insulin that drives weight gain, not the carbohydrates, so beans and bread are not equal despite the fact that they are both carbohydrates and both amylopectin.

amylopectinThe amylopectin and amylose molecules are broken down into their component glucose molecules and absorbed into the portal circulation. This is the bloodstream that takes the absorbed glucose and carries it directly to the liver.

In the liver, it is reformed into long chains called glycogen, which is a storage form of glucose (plants use amylopectin and amylose, animals use glycogen). However, storage capacity is low so the rest is turned into fat via De Novo Lipogenesis. This newly created fat is highly saturated palmitic acid, which is how high refined carbohydrate diets increase the blood levels of saturated fat, which is linked to heart disease.

Dietary protein is broken down into its components amino acids and absorbed. Some is required for protein turnover, but the amount is debatable. If you are trying to build muscle (body building) you require relatively high levels of protein. For the rest of us, a moderate amount is needed. How much? The Recommended Dietary Allowance is 0.8 g/kg lean body mass. For a 70 kg man, this is about 56 grams of protein.

For reference, this would be about 3 ounces of chicken, 3 ounces of tuna, a glass of milk and 1/2 cup of beans. That would be the protein needed for the entire day! You can see that most North Americans eat far, far in excess of the RDA. Consider that a typical burger now is 1/2 pound (or 8 ounces) by itself. There are many who argue that 0.5 g/kg is sufficient, too.

What happens if you overeat protein?

So what happens to the excess amino acids? They cannot be stored directly as energy, so they are converted to glucose via gluconeogenesis. This is a metabolic pathway that generates glucose out of non carbohydrate molecules. Here there are differences between amino acids as well. Some amino acids are able to produce glucose (glucogenic), some produce ketones (ketogenic) and some do both.

epic-studyOnce again, these amino acids are absorbed into the portal circulation and directed towards the liver where excess amino acids get turned into glucose. Since it requires liver processing, insulin is required as a signalling molecule. Since the protein does not raise blood glucose, even though it raises blood insulin, glucagon is also stimulated, as well as incretins that help mitigate this effect and prevent hypoglycemia.

It is a surprise to some, that certain proteins stimulate insulin as much as the refined carbohydrates. Animal proteins tend to have more of an insulin effect than plant proteins. There is a higher risk of diabetes for increasing quartiles of animal protein.

Dietary fat, on the other hand, is metabolized in a completely different manner than both carbs and proteins. Dietary fat is broken down into fatty acids by pancreatic enzymes (lipases) and bile salts. They are then absorbed into the lymphatic system as fat droplets (fat is insoluble in water) called chylomicrons. These do not go into the portal system and do not enter the liver. They empty directly into the bloodstream through the lymphatic circulation and then to the thoracic duct.

This is the reason why dietary fat does not require insulin. There is no further processing or handling, so insulin signaling in the liver is not required for metabolism. This dietary fat can be stored or used for energy. If you were to eat pure fat (say, Bulletproof coffee), then no glucose or protein is ingested and insulin stays low. The body then simply burns fat.

Burn sugar or burn fat

There are essentially two fuel systems for the body. You can either burn fat, or burn sugar. These two fuel systems are separate and do not interact (see Randle Cycle for more details). When insulin levels are high, then the body runs on glucose. During that period, there is simply no reason for your body to burn body fat. Why would it? It’s there in case of emergencies, in case there is nothing to eat as a store of calories. It’s like a back-up generator. If you have power in the house, then the generator stays off and none of the fat is used up.

However, if you switch to a low carb, high fat diet, then there is little glucose available to run that fuel system. In this case, the ‘backup generator’ will kick in and start burning fat for fuel. That’s great, because more than anything else, we want to burn fat.

cih-vs-ih

According to the older Carbohydrate-Insulin Hypothesis, carbs are fattening, whereas protein and fat are not. Yet grouping protein and fat together makes no sense because protein metabolism has much more in common with carbohydrate rather than fat metabolism.

The more insulin-centric Hormonal Obesity Theory leaves dietary fat distinct from both carbs and protein. Both agree that refined carbohydrates need to be restricted. However, because excess protein is converted to glucose, it can stop ketosis and weight loss efforts. So here, carbohydrates and excess protein are treated similarly, where fat is distinct. This reflects a far more physiologically accurate picture of metabolism.

So, if you eat a low-carb meal, but eat high protein (protein bars, protein shakes, whey powder etc), then your body will still be burning glucose as it ramps up gluconeogenesis to convert that excess protein to glucose. You are stuck in the ‘Burn Glucose’ fuel system. So you don’t burn fat.

You want to lose body fat? You gotta burn it off. What keeps you on the ‘Burn Glucose’ side? Insulin. It’s the insulin, stupid! The solution then, is obvious – low carb, moderate protein, high fat diets.


Jason Fung

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Video

Some people manage to lose a lot more weight by moderating their protein intake. Jimmy Moore for example, had quite some success doing that. In this membership video (free trial available) he talks about his experiences:

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Dr. Fung has his own blog at intensivedietarymanagement.com. He is also active on Twitter.

His book The Obesity Code is available on Amazon.

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16 Comments

  1. Lisa
    You talk about amino acids. I drink amino acids evution with energy once a day. I don't body build, but walk daily. Do you think that is bad, there is no carbs or sugar.
  2. James
    What is excessive protein? RDA really sound?
  3. Danielle
    "Simply put, dietary fat does not raise insulin."
    Dietary fat does raise insulin, just not as much as carbs or protein. In those who have an inflated insulin response (i.e. the obese, extremely insulin resistant, been obese for a long time) even the insulin response to fat is significant. The ONLY way for severely insulin resistant people to lower their insulin levels is the fast. I was reading diet doctor blog for many many years and following HFLC for many many years while still obese. It was Dr Fung's videos about fasting on youtube that made me realise that eating nothing is the answer to lowering insulin levels as much as possible. "Nothing" lowers insulin better than dietary fat.
    Reply: #4
  4. bill
    Absolute statements are often incorrect,
    but I'll go out on a limb and say: "nothing"
    is unsustainable. So, what are you going
    to eat when you must? If insulin is the
    issue, fat is the most appropriate food
    for sustenance.

    We don't all need to lose weight.
    There are many other reasons to keep
    insulin low.

  5. Reza Wahyu
    Gluconeogenesis is more of a constant background process, the rate for gluconeogenesis process is unaffected by excessive protein intake.

    So excess protein won’t be stored as glucose or fat.

    Gluconeogenesis from protein is a costly process for the body, better breaking down the triglycerides.

    Excess protein will be built in as your muscle mass if you exercise, be oxidized as energy sources, and the nitrogenous waste of urea will be thrown in the urine..

    References

    1. McGuire M, Beerman, KA.: Nutritional Sciences: From Fundamentals to Food. 2nd edn. Belmont, CA.: Wadsworth Cengage Learning; 2011.
    2. Gropper S, Smith, JL., Groff, JL.: Advanced Nutrition and Human Metabolism. 5th edn. Belmont, CA.: Wadsworth Cengage Learning; 2009.
    3. Bray GA, Smith SR, de Jonge L, Xie H, Rood J, Martin CK, Most M, Brock C, Mancuso S, Redman LM: Effect of dietary protein content on weight gain, energy expenditure, and body composition during overeating: a randomized controlled trial. JAMA 2012, 307:47-55.

  6. 1 comment removed
  7. Chad
    The protein RDA example in this article appears to have an error. The article states the RDA is 0.8g/Kg of lean body mass. The example then uses the total mass of the 70kg man instead of the lean body mass to get a result of 56g of protein.

    This is a very interesting article. What if you are trying to build muscle not just maintain? What would you recommend the RDA to be? 1g/Kg of lean body mass?

  8. Kathy from Maine
    Even if some of the protein does turn into glucose, why is that so bad? If you're eating a low-carb/whole food "diet," you have a few carbs to spare.

    But let me get this straight. I'm trying to lose weight, so:

    I don't want to eat too much FAT, because then my body won't burn my body fat.

    I don't don't to eat too much PROTEIN, because it will turn into glucose and trigger the insulin and keep me fat.

    I don't want to eat too much in CARBS, because it will definitely turn into glucose and trigger the insulin and keep me fat.

    Is it any wonder I seem to have no clue anymore what I'm supposed to eat, and how much? Trust me, I'm not trying to be funny here. I'm less sure what to eat now than 20 years ago when I first learned about low-carb eating.

    Reply: #9
  9. bill
    Kathy:

    I agree with you. This site has lost its focus.
    Too much emphasis on IF and other such
    unnecessary nuances.
    Dr. E needs to return to the core message
    that it is Low Carb, High Fat.

  10. Barb
    Kathy:
    I agree with you also. 15 yrs ago, I lost 40 pounds doing the "Atkins diet". I didn't realize then that when I hit a plateau it may have been a "normal" thing. After weeks of not losing anymore, I slowly reverted to my muffins & cookies & bread. Big mistake! I've gained about 25 pounds of it back. Then, this year I found Diet Doctor. I really appreciate this site & I believe LCHF does work. I've lost some weight (don't really know how much as I don't depend on the scale anymore) & have lost inches too. But now, after reading a lot on here, (IF, etc, etc.) I don't know what I should or should not be eating or the amounts. I do believe in Intermittent Fasting, but it's just "not eating". I do think low-carb eating is the way to go, but sometimes feel inundated by too much & don't know which way to turn.
  11. Kathy from Maine
    Thanks for the support. I lost about 25 pounds when I discovered Atkins around 1998. The weight literally fell off me. I went from 175 to 150 with hardly any effort. I lost it so quickly my husband kept asking if I was sick. Nope, I felt GREAT!

    Now, after 20 years of reading all the books, blogs, etc., I can unhappily say I'm now 20 pounds heavier than when I started back in 1998. How can that be? I follow the rules (about 90/10 percentage), I rarely eat processed foods, and instead rely on whole foods. I keep my carbs low. I eat only healthy fats. I eat quality protein.

    Only when I'm 100% on plan do I lose pounds/inches, albeit ever so slowly. If I loosen up the tiniest bit, I gain it all back with a vengeance. It can take me 2 months to lose 5 pounds, and 1 week to gain it back if I'm not watching every single bite. And trust me, I'm not binge eating to gain that 5 pounds or more back in a week; I'm having maybe a glass of wine a couple nights a week, or even just eating a slightly larger portion of the same foods I ate to lose the weight.

    I've come to the the conclusion that I "broke" my metabolism/hormones/whatever somehow. Otherwise, these measures would still work. So how do I "un-break" these things?

    I'd love some of the experts on this and other sites address these issues and attempt to explain why this is so. And it's not just me. I hear the same thing all the time on the various low-carb forums and discussion groups.

    Reply: #12
  12. Marianne G
    Kathy, I could have written your post myself.... I also lost on Atkins years ago with ease and now I'm heavier than ever and it's a struggle to lose. I think part of the issue is simply the passage of time. We're 18 years older than in 1998, after all. Broken metabolism? Maybe. Certainly damaged, in my case (I'm pre-diabetic). But in the past 3 weeks I've lost 6 lbs, which for me is super fast! I did it with intermittent fasting. Dr Jason Fung is a lifesaver, his book The Obesity Code is a revelation. I think I am finally going to be able to heal my insulin resistance.
  13. bruce
    I don't want to throw a wet blanket on this newer gen theory of fat metabolism, but I too lost over 50 lbs on Atkins 15 years ago. I went from 235 to 177 doing nothing more than LFHC. I have major depression and other issues so during that time I was in the bed. I did NO exercise during this period. I just followed his advise very strictly (25g)CH/day until goal reached then add in CH as able. Watching the ketostix is critical to keep it off and a tremendous incentive to keep going. I kept the weight off for 10 years and got fit like never before. Unfortunately my mental health issues have become much worse and I wasn't able to continue eating the Atkins way. If there is a better way, use it, but I swear by Dr Atkins.
  14. Barry Davidson
    So you give link for where they have been proven wrong about carb and fat intake. http://www.health.harvard.edu/blog/how-much-protein-do-you-need-every.... Why are they right about protein?
    Reply: #15
  15. Tim
    Yeah, as well as telling me to eat protein at .8g per kg of body weight, they want me to eat 366 - 528 grams of carbohydrate, according to their calculator.
    They operate in the same realm as witchdoctors, on belief...not much credibility there. If you want to make an argument about protein, use credible sources.
  16. Josh
    When I eat excess protein, does gluconeogenesis kick me out of ketosis like if I ate sugar where I am kicked out of ketosis, or does gluconeogenesis behave more like alcohol does when I drink i.e., the body uses the alcohol as energy until all of the alcohol is burned off but then goes right back into ketosis?
  17. Mandy R
    The studies I found say this does not happen, and protein intake does not affect the rate of gluconeogenesis at all. I don't see any citations here of any studies supporting this stance either. This is a "theory", and not even a logical one. If there are studies I can't find that state otherwise, I'd like to see them. Otherwise I will continue to see this theory as unsupported and invalid.

    "Gluconeogenesis is more of a constant background process, the rate for gluconeogenesis process is unaffected by excessive protein intake.
    So excess protein won’t be stored as glucose or fat.

    Gluconeogenesis from protein is a costly process for the body, better breaking down the triglycerides.

    Excess protein will be built in as your muscle mass if you exercise, be oxidized as energy sources, and the nitrogenous waste of urea will be thrown in the urine..

    References

    1. McGuire M, Beerman, KA.: Nutritional Sciences: From Fundamentals to Food. 2nd edn. Belmont, CA.: Wadsworth Cengage Learning; 2011.
    2. Gropper S, Smith, JL., Groff, JL.: Advanced Nutrition and Human Metabolism. 5th edn. Belmont, CA.: Wadsworth Cengage Learning; 2009.
    3. Bray GA, Smith SR, de Jonge L, Xie H, Rood J, Martin CK, Most M, Brock C, Mancuso S, Redman LM: Effect of dietary protein content on weight gain, energy expenditure, and body composition during overeating: a randomized controlled trial. JAMA 2012, 307:47-55."

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