When Is A Calorie Not A Calorie?

Im really excited about today’s guest post.

Not only am I a bigbig fan of Darya’s blog —-I love and admire her ability to explain science in a clear, concise & *understandable* fashion.

Thanks so much Darya for making time to explain what I totally could not respond to a MizFit reader comment.

EDITED TO SAY: The initial post can be found here.

•  Anne Keckler | ACSM Certified Personal Trainer Says:
March 24th, 2009 at 9:32 am
The cleaner you eat the more calories you can consume while not gaining weight.
I’d like to have a scientific explanation of this.

I just want to start by saying, I LOVE a skeptical reader. Kudos to Anne for requesting facts to support this unconventional wisdom offered by MizFit.

While it seems pretty safe (and within the laws of thermodynamics) to say that a calorie is a calorie, and that “calories in must equal calories out,” this is actually an oversimplification of the way our bodies work.

To put it simply, a calorie IS a calorie, but how your body uses that calorie is dependent on context. In other words, the way those calories are delivered to you (i.e., the food you eat) can affect how your body metabolizes them.

There are three ways your body can deal with a calorie. It can use it immediately, it can store it, or it can skip digestion and let it go untouched. Fiber is a good example of something you cannot digest. Any calories locked in fiber (not calories surrounded by fiber, but the fiber itself) will not contribute to your metabolism.

When we talk about “using” a calorie, most of the time we are referring to burning glucose as fuel in muscle tissue. When we “store” a calorie, it means the glucose (sugar) was converted to fat and placed in special tissue called adipose.

But what determines whether we use or store a calorie?

Under normal circumstances this decision is made in the blood. When you digest food that contains calories, your gastrointestinal system converts the carbohydrates you have eaten into blood glucose. It turns out that how quickly this happens is extremely important for how your body deals with those calories.

Most of us would prefer that all the calories we eat go directly to muscle fueling and not to fat storage. Better muscle fueling causes us to burn more calories involuntarily—this is your “metabolism.” What and when we eat determines how effectively we fuel our muscles. Any extra glucose that is not burned is converted to fat and stored.

Glucose can only enter (fuel) your muscles in the presence of a hormone called insulin. Insulin is produced by your pancreas in response to high blood sugar (i.e., after a meal). But your muscles can only detect insulin if they have insulin receptors. Think of insulin receptors as the lock and insulin as the key to let glucose into your muscle tissue. How much glucose can get in at one time depends on the size of the door.

Make sense?

The scientific term to describe the size of the door is insulin sensitivity.

Your body tries its best to maintain stable blood glucose and insulin, so when there is a rush of blood sugar it is in a hurry to get it out of the blood ASAP. If glucose cannot get into muscles fast enough (option #1), it is whisked away into fat (option #2) to return levels to normal.

We all have a set level of insulin sensitivity right now. The more insulin sensitive you are, the more glucose can fuel your muscles at one time. But if you are insulin resistant, your insulin door is easily jammed up with extra glucose. This causes the calories that would have been burned as fuel to be stored as fat.

But it is important to remember that no matter how insulin sensitive you are too much glucose at the same time can overload your muscles and cause extra calories to be diverted from your muscles to fat. You do not have to be insulin resistant to force fat storage.

Conversely, if you stretch out the same amount of glucose and insulin over a longer time period (a long, slow peak rather than a spike) those same calories can be burned as fuel in your muscles instead of being stored. This is equivalent to glucose getting in a single file line to fit through the door rather than trying to force its way in like an angry mob.

To summarize, a calorie is not a calorie when you have a blood glucose and insulin spike that forces it to be stored as fat rather than used as fuel.

What causes a blood glucose spike is a meal loaded with quickly digesting carbohydrates. These foods are very rare in nature, but are abundant in our Western culture and are called processed or refined carbohydrates.

Another nutrient that can negatively impact your insulin sensitivity is saturated fat.

When Miz says she tries to eat “clean” food, it is less processed and therefore less likely to cause a blood sugar spike. Based on her daily diet, she doesn’t eat much saturated fat either.

If your muscles are stressed too often with excess blood sugar the number of insulin receptors will decrease, your glucose door will shrink, and you will become more insulin resistant. This has both short and long-term effects. Spiking your blood sugar at breakfast will make you more insulin resistant at lunch. Stretch this over years and you develop type 2 diabetes.

If that does not scare you enough, insulin signaling is also strongly linked to more rapid aging. So not only do blood sugar spikes make you fat and give you diabetes (and probably heart disease), they are making you older too.

Fortunately, the vast majority of delicious foods on this earth do not promote blood sugar spikes. You can eat all the vegetables you want (fruits are a little sweeter, but still very good for you). Whole, intact grains take so long to digest that they beautifully distribute your blood glucose peak over several hours, helping you avoid a glucose spike while providing perfect muscle fuel. Lean meats like fish and poultry have almost no impact on blood sugar and contain little saturated fat.

Finally, what you eat can also contribute to the number of calories you want to eat. A well-fueled, nourished body does not crave sugary, processed foods because it already has what it needs.

If you are eating a variety of whole, mostly plant-based foods, the calories you eat are very different from the ones you would get from junk food. This is not because of the calories themselves, but because of how your body deals with them.

Darya is a scientist, San Francisco foodie and advocate of local, seasonal foods. Summer Tomato offers tips and advice on healthy eating, especially for foodies in urban areas.


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  1. says

    Awesome that this is being addressed. Love the explanation and the clean eating healthy food promotion.

  2. says

    I just cannot tell you just how perfect timing this article is! Tahnk you Miz for hosting and Darya for the so clear information I ahve been researching actually for weeks and have NOT come across it explaind so clear and so easy to understand.

    So with the quote below in mind….
    “If your muscles are stressed too often with excess blood sugar the number of insulin receptors will decrease”

    ….is there a way, is it possible to reverse that? So the muscles have more insulin receptors?

    Thanks again!

  3. says

    What a wonderful way to explain this concept! Thank you Darya and Mizfit! I’m basing my own eating habits on this concept – mostly plant-based whole foods – and am really pleased with the results in terms of weight loss, increased energy and health improvements.

  4. MizFit says

    I just wanted to echo everyone else and say THANK YOU again for such a great explanation of a tough to distill concept.

  5. Bea says

    This combined with the post Miz did on her eating clean NOW makes total sense.

    I am trying not to eat for how I will look BUT if I do cut out the processed foods and even increase my calories based on this I will look even better (more lean)?

    Is that correct?

    It seemed to me that that was what Miz was saying as well?

  6. says

    Wow, what a lucid explanation of a really complicated subject!

    I’ve been trying to eat this way for other benefits, didn’t realize it could actually help discourage fat gain.

  7. Nancy says

    Lots to process and I had not read the first post either.
    Thanks Darya and Miz.

  8. dragonmamma/naomi w. says

    Great explanation.

    Plus, don’t forget that protein is more thermogenic than fats or carbs. That is, the body actually burns more calories in the process of digesting it.

  9. says

    Love this! A lot of times I hear the same thing over and over from fitness peeps. I know they are right but they can never explain WHY they are right. It is nice to understand the science behind things. Good post!

  10. says

    This was a great explanation of a complicated subject – one that I’ll definitely have to remember for later! (My attempts to explain it often only make sense in my head, but not so much when they leave my mouth, LOL.)

  11. Evan says

    Awesome post. I am with Marste in that I get it (or thought I did) and can never explain it to others.

    Thanks Miz and SummerTomato!

  12. says

    This is a wonderful explanation of this much misunderstood subject. You can see now why labels on food display saturated fats along with sugar content. One of the nice things I’ve been told is that much of Insulin resistance can be reversed with a well thought out diet along with exercise to burn the excess stored glucose.

  13. says

    This really was a very clear explanation of a very complex project. I am going to bookmark this for future reference. (because I know I will forget and will not be able to explain all this to friends.)

  14. says

    Great, informational post. I have the Eat Clean Diet book to read once my liquid fast is over – or better yet – to read now.

  15. says

    Great post! Thank you for the information. Is there a certain level at which your insulin level causes calories to be stored as fat, or does it vary depending on the person?

  16. says

    Fabulous post. Well written and so damn informative! I’ve (kind of ) intuitively understood how this all worked, but could never put it in words.

  17. says

    This blog is always so chock-full of great and useful information. Thanks again for a job well done – always.

  18. says

    Thank you for this explanation! Not only does it clearly explain something I’ve found to be personally true (but hard to understand), I LOVE the way you talk about food, Darya. Wow, and her blog is beautiful…um, I may have to disappear over there now. :)

  19. says

    For the 34th (or 35th if someone else jumps ahead of me) time…great explaination! Thanks for clearing things up :)

  20. says

    Thanks everyone for your feedback! I’m glad I could help the Bumbling Band get a little sciency this morning. The only Internet access I have right now is my iPhone so sorry if these replies have some typos.

    @berni I’m not sure there is an easy way to test insulin sensitivity, but fasting glucose and insulin tests they do to test diabetes is usually how doctors check for metabolic dysfunction.

    @trish Yes you can reverse insulin resistance, great question!! You can improve insulin sensitivity with exercise and by maintaining stable blood sugar (e.g. eating well).

    @Miz Thank YOU for this opportunity for me to show off what a nerd I am!

    @Bea Yes!! You will increase your metabolism and burn fat. I’ve lost more weight than I even wanted to eating like this. It is also the most delicious food ever!

    @Nina insulin sensitivity is different for everyone. It actually varies for one person over the course of the day. A really bad meal can mess up your metabolism for up to 9 hrs after eating. If u email me I can send u a link to an article I wrote on this when I get back on a real computer.

  21. says

    Darya, you rock! Thanks, MizFit for getting to the bottom of this. From my research, it seems insulin (and insulin resistance) is just one car in a very long hormonal train…and can be greatly affected by adrenal gland performance and fluctuating estrogen and progesterone, as well. Clean eating, and stress-free livin’ seem to be the keys. Thanks again.

  22. says

    Wow, this is a terrific post! Thanks, Darya! I’ve got a question, though: you stated that saturated fat can negatively impact your insulin sensitivity. How does that happen?

    Regarding testing one’s insulin sensitivity, I believe the glucose tolerance test is done for that. (There are other tests, but I think this is the one that’s most commonly done.) It’s kind of time-consuming: you drink a nasty, sweet beverage, and blood is taken at regular intervals to see how your body is processing the sugar. Alternatively, though not a measure of insulin sensitivity per se, the HbA1c test measures how well your blood glucose has been in control (i.e., has it been consistently high or normal?) over the 3-4 months prior to the test. The advantage is that it’s a simple, quick blood test, and sometimes pharmacies offer this in conjunction with low-cost cholesterol screenings. (The HbA1c is a regular part of the type 2 diabetes care regimen.)

  23. says


    Thanks for the great post. I’ve wanted a detailed scientific explanation of that for a while now. As one nerd to another – thanks :)

  24. says

    quick question – it this whole insulin spike issue another reason for why it is better to be eating small meals throughout the day instead of a few big ones? This keep the levels more even yes?

  25. says

    I agree that it is not as simple as calories in, calories out. Yes, it is more complicated than that & a woman my age knows that! I have to agree that I have eaten similar calorie counts in a day but not the foods I am eating now and I have not been as lean nor my body as low. It is a complicated process & we all have to find that balance that works for us & we can live with long term.

    Great post!

  26. says

    Thanks for the thorough explanation! Lately, I’ve been trying to pay attention to how I feel after eating certain foods, and it is really interesting. I have never done that before. I will never give up my beloved chocolate, but other than that, I’m pretty “clean.”

  27. MB says

    Clear and concise. Well done. I echo the question of how to increase insulin sensitivity.

  28. says

    Awesome post!! Great way to explain calories. Now I need my friend to read this (who is trying to lose weight, but only eats lean cuisines and 100 calories packs).

  29. says

    I’ve noticed that when I eat too many sweets I develop a little fat on my stomach, even if my overall calories are about the same. I always heard “a calorie is a calorie,” but now I know that little pooch isn’t in my head!

  30. says

    @pubsgal from what I have read saturated fat can hinder insulin signaling by integrating into the cell membrane and disrupting insulin signaling at the receptor level (insulin receptors span the cell membrane).

    @MB Check out my blog post from May 13 about exercise and insulin sensitivity. Generally eliminating insulin spikes with sensible eating is also necessary.

  31. says

    I love this post and have been reading it for the past 4 hours so I can absorb the info.
    Thanks. I love a good scientist. I also visited summertomato and can’t believe this scientist ate a hotdog.

  32. says

    Most Excellent. Now I am filled with renewed determination. I’m also going to print this out for ScottieDog, the “junkie” (not the narcotics kind!).

  33. says

    @POD I LOVE hot dogs! Although I don’t eat them often I am a strong believer that you cannot deprive yourself of foods you love.

  34. says

    Mizfit, I need your help! Usually I am sedentary lifetyle person with a rigorous workout schedule. I work out about 6 days out of 7, and each workout is intense, involving spinning, running, HIIT etc. BUT i would like to lose these last 15 pounds (No..not vanity pounds) .
    Another factor is my summer job! Like I said..usually sedentary, but in the summer I work for grounds, namely 8 hours of weeding, planting, raking, hoeing etc 5 days a week.
    I cannot figure out how many calories I should be eating!
    I also plan to workout pretty intensely about 4 days of the week.
    Oh am 5’0 and weigh about 140.

  35. says

    Wow, what a great explanation! Thank you!

    Miz, funny to see this post today – I was thinking about you earlier today and wondered what you eat exactly. Care to post a daily menu or a “day in the life of Mizfit” ?? I would love to see your eats!

  36. suganthi says

    This is a great read. Do the number of insulin receptors actually decrease with excess substrate?

    I did like to hear your/Miz’s take on the fact that that I saw somewhere : strength training is more effective for controlling sugar rather than cardiovascular exercise.

    I realize that in reality, this is a very complex process. I grew up on a vegetarian South Indian-based diet.. plenty of white rice, loads of high fat fried foods (not on a daily basis, but we did it whenever we had to celebrate which was often). Even though vegetarian, we tended to have it as a smaller side relative to the not good stuff. It has taken years of nagging from my husband for me to really believe it, to cut down on white rice. Diabetes has become very common in India. Paradoxically, none of our older generations seemed to suffer from this, long lives with not a great deal of exercising. This statistics is based on just our extended family members not a whole popuulation statistic ;). And I see a whole range of phenotypes : people who truly eat decadently and are rail thin, people who don’t eat much at all and have developed diabetes and are obese. Genetics does seem to play a part.

  37. suganthi says

    Oh no! I just visited Darya’s site. Fantastic! Where the heck do I find time to keep up with all of you wonderful folks.

  38. says

    This is facinating, just going to read the original post. Thank you for such valuable information! I’ll have to re-read it again but I appreciate you making it as reader-friendly as possible!

  39. s says

    cool, informative entry. gives me some good reasons to go for more clean, not-as-processed foods more often.

  40. says

    Awesome explanation. Thanks. I’m off to read your previous post on exercise for insulin resistance. I want to open those doors to let the glucose into my muscles because sometimes they suffer from fatigue before they even do anything! Makes it physically difficult to exercise sometimes.

  41. says

    I’m also a little late in on this but wanted to say what a great post this is on a complicated topic.

    This is a concept that I’m quite familiar with but yet admit I still didn’t understand enough to explain myself. This post made such sense.

    Here in Oz a lot of our food is labelled to indicate how it is on the Glycemic Index (a ranking of carbohydrates according to how quickly they effect blood sugar levels) http://www.glycemicindex.com/ & http://www.gisymbol.com.au/GIFlier08.pdf – there’s been a real drive towards low GI food here, do you have similar there in the States?

  42. says

    Great explanations- love the door metaphor, very helpful. I have been eating “clean” for a while, and help my clients with this as well. I also like Dr. Mark Hyman’s explanation that our body doesn’t know what to do with processed foods- b/c we didn’t evolve on all these things, our body doesn’t know how to properly or efficiently metabolize them if it comes in boxes/bags or has labels!
    Another piece of recent research is the link between insulin and Alzheimer’s- link so strong they are now calling Alzheimer’s “type 3 diabetes”.

    thanks Darya and Carla!!

  43. says

    “from what I have read saturated fat can hinder insulin signaling by integrating into the cell membrane and disrupting insulin signaling at the receptor level (insulin receptors span the cell membrane).”

    Do you have a source on this? I’m extremely skeptical here–saturated fats are a necessary part of cell membranes, comprising 50% of the structure. What’s the suggested mechanism by which saturated fatty acids hinder the function of insulin receptors?

    Beyond the one sentence I have issue with, great article! The world would be so much healthier if people understood these principles.

  44. janice says

    Thank you K., for asking for clarification on the saturated fat sentence that is begging for further explanation. lately its been occurring to me, for many reasons that the sat fat thing is bunk, not the least of which is our evolutionary history. we ate lots of saturated animal fat before the agricultural revolution. it does not seem adaptive that a primary source of nutrition would actually be bad for human health – that just doesn’t make any sense at all!

    Darya, why do you remain convinced that sat fat is a dietary evil?

    cheers to good health!


  45. says

    Fiber does so much more than just not be absorbed too. It actually burns calories as it works its way through your digestive tract! Your body has to push that fiber through your system, exercising your involuntary muscles and also pulling toxins and undigested food with it. Each gram of fiber actually burns 7 calories!

  46. Altaf Adam says

    Great post, but 2 questions??? You say that Saturated Fats also effect insulin. I thought FAT is insulin neutral? second, if I eat a rich breakfast, I understand insulin will remove and store it quickly as fat. But then, if I eat my lunch 3 hours later, will not the energy during this 3 hour period be released from the fat storage? If it is released from other sources (liver, etc.) won’t energy still be released from the fat storage to make up for what is released from other sources?


  1. […] It could be said that I am one of the lucky ones who doesn’t have any strings attached to my eating. I am not an emotional eater, and I do not have binging issues. For me, the “burn more than you take in” approach worked until I was diagnosed with insulin resistance and polycystic ovarian syndrome in September 2008. Then it became a matter of counting the right kind of calories. […]