The common currency in our bodies is not calories – guess what it is?

Currency (money) is useful because it represents mutually agreed upon means of measurement and exchange. That is, if we all accept American dollars as our currency of exchange, then items as disparate as a bus or an onion can be all measured in the same units.

The bus is expensive and costs more dollars and the onion is cheaper and costs fewer dollars. But everything is measured in dollars and both parties accept dollars as the currency of exchange.

If one party decides to deal in dollars and the other accepts sea shells (as used historically in some primitive cultures) or salt, then it is impossible to deal. There is no common currency. The buyer wants to use dollars and the seller wants sea shells. No deal.

Both parties need to agree on how to trade. That is the value of a common currency, whether it is dollars, sea shells, Bitcoins or gold. There is only power as long as the two parties agree.

It is just like a common language. English is particularly useful because many people speak it. Therefore, in the United States, it is very likely that you can speak English and somebody understands you. In China, Mandarin is more useful than English, again because both people are able to speak it.

BobMicrosoft dominated the software wars because it was the most popular, which automatically made it the most useful. It sure wasn’t the blue screen of death, or Microsoft Bob that made it useful. Man, I hated that stupid paperclip. Made me want to poke my own eyes out. But Microsoft was the common standard, which made it useful.

The common currency of weight gain

But this post is about nutrition and obesity. So, what is the common currency of weight gain? Most people think that ‘calories’ fulfills this role of common currency. Sugar contains a certain number of calories and lettuce has fewer calories. We imagine therefore that these calorically ‘expensive’ and ‘cheap’ foods can be measured on the same currency of calories.

There are other ways, of course to measure different foods. You could simply weigh them. So 1/2 a pound of sugar is the same as 1/2 a pound of lettuce. This is simply a different currency. You could make the same First Law of Thermodynamics argument for weight as for calories.

If you eat 1/2 pound of food, whether sugar or lettuce, you must gain 1/2 pound of weight. After all, how can your body gain more weight? Does weight come from thin air? How can it gain less weight? The weight of food simply disappears?

Thermodynamics is a law, not a general suggestion. In both cases (weight and calories), the confusion arises from misunderstandings about thermodynamics and body fat.

What’s crucially important, though, is to see if the body ‘cares’ about calories. Does the body have some mechanism to count calories? Does the body have sensors to detect calories? Do we have an internal bomb calorimeter to measure calories and change behavior/ metabolism based on calories? No, no and no.

200 calories

200 calories

Your body doesn’t give a hoot about calories. Calories are not an accepted currency in our body. It does not count calories so why should you? A calorie is a calorie. So what? Who cares? Certainly not your body. Consider two foods of equal caloric value. On the one hand, you have a bit of sugary soda, and on the other is a plate of lettuce. Calories are identical. OK. So what? When you eat those two foods, does your body somehow measure these calories? No.

The metabolic effect of those two foods is completely and utterly different. Sugar will stimulate insulin. It will not activate any of the other satiety hormones. It does not activate stretch receptors in the stomach (satiety signal). It does not activate peptide YY, cholecystokinin (satiety hormones). A piece of steak, on the other hand, will do all those things. Therefore, you feel full after eating the steak, but not sated at all with the soda.

Our bodies don’t count calories or weigh food

So, why do we pretend that all calories are equal? There’s nothing equal about them. Calories are not the common currency of the body. It’s like we’re walking around with a bunch of sea shells in our pockets and trying to buy a hamburger in Philadelphia. Everybody wants dollars and we want to pay in sea shells. The burger guy doesn’t care about sea shells. Our body doesn’t care about calories.

The same applies to the weight of food, or the volume of food.

Your body doesn’t weigh the food coming in, and doesn’t care. The key is that eating a pound of lettuce and a pound of sugar produces completely different metabolic responses. In one case, the body may burn off that energy, and the other case, it may decide to store that fat. Weight is not the common currency.

No, our body gains or loses fat according to detailed hormonal instructions from our brain. So what does our body respond to? Insulin. The rise and fall of insulin is the main stimulus to weight gain. So, foods that stimulate insulin are typically more fattening (cookies). Those that do not (kale) are typically not fattening at all.

If the body cares about insulin (and other hormones, but mostly insulin), then we need to use the common currency, speak the common language of the body. Insulin. We can translate foods into insulin effect instead of calories. Marty Kendall at Optimising Nutrition did just that.

Insulin index

Insulin index

Insulin index

He has constructed the best food insulin index available. You can estimate a foods insulin effect based on net carbs (carbs- fibre) + 0.54 protein. Even then, this formula only accounts for about 50% of the known insulin effect, so there is still much more we need to learn. The least insulinogenic diet is low carb, high fibre, moderate protein, high in natural fats. In other words, a real food, LCHF diet.

GLThe same goes for counting carbohydrates. You body certainly responds to carbohydrates, but it doesn’t count them. Some carbohydrates will stimulate insulin and others will not. That means that all carbohydrates are not equal.

Highly processed carbohydrates are very stimulating to glucose and insulin. Minimally processed carbohydrates have very little glucose or insulin effect.

So remember, the common currency of the body is not calories. But neither is it dietary fat, protein or carbohydrates. It’s not fibre. It’s not ketones.

The only currency the body really cares about is insulin. If you want to lose weight, reduce insulin. If you want to gain weight, increase insulin. That’s the common currency. Since our body only cares about insulin, we better learn the insulin effect of foods.

Jason Fung

Top videos about insulin

  • How to maximize fat burning
  • Part 8 of Dr. Jason Fung's diabetes course


A Low-Carb Diet for Beginners

How to Lose Weight

Popular videos about losing weight

  • How to maximize fat burning
  • Living low carb with Sue Acres
  • Living low carb with John Holding
  • "I'll do this or I'm going to die trying"

Earlier with Dr. Jason Fung

Why the First Law of Thermodynamics Is Utterly Irrelevant

How to Fix Your Broken Metabolism by Doing the Exact Opposite

More with Dr. Fung

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

His book The Obesity Code is available on Amazon.

The Obesity Code


  1. Thiago
    Could a diabetic control your blood sugar by eating real food regardless of the composition ( carbohydrates, fats and proteins) , so?
  2. Maura
    Terrific explanation, including that remarkable photo of '200 calories =...'
  3. PJinLA
    Great article.
  4. Apicius
    Hang on. I have a hard time accepting boiled potato, sweet potato and brown rice as whole food category. They should all be in the processed food category. You don't pull boiled potatoes out of the ground, and the rice goes through a husking process followed by being boiled before it us consumed. If you can yank it out of a tree (or a plant or from the ground) and can immediately peel/eat it, then yes I can qualify that as whole. Boiling, industrial husking, etc, is processing.
  5. Agnes
    I also hated that paperclip.
  6. Joy
    Excellent explanation!! Definitely going to share this.
  7. Macghie
    I am exceedingly impressed with this article. Explains the process in a way that anybody should be able to understand.
  8. Tomm
    what does this mean for a diabetic taking insulin every day?
  9. Juan Noval
    So, as a T1 diabetic who needs to take insulin there's no hope for weight loss? Any suggestions or helpful hints?
  10. Alek Steel
    This doesn't make sense to me as it doesn't explain the most common reason people don't lose weight while eating LCHF, which is taking in too many calories from fat. We know that fat doesn't trigger an insulin response. Therefore, by logical extension of reason, one should be able to eat a pound of butter or coconut oil and since it doesn't trigger an insulin response, it won't cause weight gain. We know that to be false. Calories do count. If the body receives more calories than it needs (even if as pure fat), it wont burn stored body fat. It will remain in ketosis but it won't release stored fat because it has excess fat coming in. In fact, in this scenario one would gain weight. Therefore, insulin can not be the only currency. Would love an explanation from a physiological perspective.
    Reply: #16
  11. Jo
    We do know that even fat triggers an insulin response, just to a lesser degree. Possibly insulin release is dose related (that would be my guess). It's pretty hard to sit down and eat 450g of pure butter or any solid pure fat (I tried the other day- can't comment on drinking it). It's not tricky to eat a family block of chocolate (again, I've tried and succeeded many times there!). So, dose +/ - foods that trigger high insulin = more insulin = weight gain. That's my lay man's interpretation :)
  12. gbl
    I like your style JO. I might test this with bars and blocks of different brands and chocolate content and call it a study.

    I've certainly experienced the too-much fat response in one go making me sleepy. And confused. I thought it was only sugar/grains that were supposed to do that. N/2

  13. Darlene b
    Dr. Fung, thank you so much for this brilliant but easy to grasp explanation of how our bodies function with regard to metabolizing food. I wish you would send this to every dietitian and nutritionist in the world as they are some of the worst purveyors of misinformation in the health profession. Well, no maybe endocrinologists rank just as high. I am totally healthy, on no medications and lost 60 lbs after 7 months of being very low carb. I am 66 and now work out intensively 6 days a week lifting more weight than i did in my 20's. This, after being diabetic for twenty years. Thank for your highly Informative presentations and thank you for believing that ordinary people do want to be informed and can grasp science based concepts if presented with clarity.
  14. Kristal
    Dr. Fung, I love your work but this chart is confusing, or a better explanation of what the "Insulin Index" actually means is needed. According to the data points, steak and white fish have a higher insulin index than navy beans, All Bran, porridge, pasta, and raisins. An equation that only accounts for 1/2 of what is going does not appear to be an accurate depiction of reality to me, and is actually contradictory to most of the advice on this blog. If insulin is the only currency, then steak and white fish should be more weight-gain promoting than All Bran and pasta, which we know is not true. The only thing the chart helps with, is to say that raisins are better than jelly beans, or full cream milk is better than steak, etc, in terms of less insulin response.
  15. dan rn
    Dr Adkins made his millions on this principle: dietary fat is not utilized as calories in the human body. The principles of his book show the decided difference in the acytl coa and krebs cycle of bodily energy production. Science proves the veracity of the fact: our bodies do not treat calories as bunsen burners.
  16. Connie Cason
    It's not about the calories in the fat that you eat. It's about the amount of fat you eat. Fat is fuel. If you eat the amount of fat your body needs for fuel, you won't burn body fat, therefore you won't lose weight. If you eat 1/2 of the amount of fat your body needs that day for fuel, then your body will get the other 1/2 from stored body fat causing you to lose weight. It's not about calories. It's about fuel. If you keep your insulin low your body will burn body fat (stored fuel) if you aren't eating too much fat (fuel). I hope this helps you understand.
  17. Maria
    But...people who become vegan almost always loose much weight, is it then because they lower their insulin even if they eat almost only carbs..?
    Reply: #18
  18. Vanja
    Most of the vegans I know are quite fat.
  19. Dan
    I was vegan for five years. I put on 20 pounds. I resumed a carnivorous diet, specifically LCHF. The weight came right off in 3 months. The problem with the vegan diet is that you assume you’re being so healthy you can permit yourself unlimited quantities of any “allowed” foods. In my case, Oreos and beer. The insulin hypothesis of fat storage precisely explained my heavier state and showed me the way to a quick remedy.
  20. Claire
    This does not make sense. Butter, bacon, fat? Those kind can cause blockages in the arteries, cardiovascular diseases and increase heart attacks. I'm from a small town where everybody knows everybody. I know men and women who have had triple bypass or heart attacks because they ate animal meat on a daily basis. For me, I can eat a lot good carbs and lose weight, and gain if I eat the bad ones. I have put a few diets together (whole-food plant based and GI) that I found to be the best for me.

    Also, I think the insulin graph is a good start, but incomplete. There should be other factors included like food density, just anything. The same graph can be used to show a correlation between animal meat consumption and heart attacks.

  21. Kenneth
    Good article Dr Fung. I’ve been preaching this exact concept for over 20 years. When I was in JR High, over 40 years ago, my older sister read “The Carbohydrate Addicts Diet” which predates Atkins by several years. Then when I was in my first undergraduate Biochemistry class, I learned about how insulin controls phosphorylation of metabolic enzymes, controlling the balance between fed and fasting metabolism. I was hooked. I will be in Austin in October at the WorldLink conference. Neal Rouzier is my mentor and a very close friend. I hope to meet you there and talk over some of the details. Thank you for what you do. Kenneth Wilgers, MD

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