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The personal blog of Peter Attia, M.D.

You are not what you eat

You are not what you eat
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You are what you eat, right?  How many times have you heard this?  I’d need scientific notation to actually enumerate the number of times I’ve heard this statement or one like it.  I certainly spent most of my life believing this, too, without ever questioning it. In fact, this you-are-what-you-eat dogma plays a significant role in our misguided belief that fat is bad for us.

So let’s examine this “dogma” and let’s use an average person as an example:

  • Assume you consume 2,500 calories per day
  • That works out to over 900,000 calories per year
  • Let’s assume you gain one pound of fat in a year (the average American does this beginning at the age of 25)
  • One pound of fat is equivalent to 3,500 calories of stored energy
  • At the end of the year you’ve gained 3,500 calories worth of energy out of over 900,000 calories ingested
  • In other words, you burned off more than 99.6% of the calories you consumed and only stored less than 0.4%
  • This works out to an average of less than 10 calories per day that we “store” in this scenario of gaining one pound of fat per year


What should you take away from this?  For starters, we burn almost all of what we ingest.   There are, more or less, four ways we account for this combustion of energy: digestion, activities of daily living (e.g., carrying your groceries, walking up the stairs to your apartment), exercise (the deliberate activity we do, say, going for a run), and resting metabolic expenditure.

The last of these is almost certainly the most important.  Why?  In most people, it accounts for the greatest “sink” for calories.  It’s always “on”. In other words, our resting metabolic expenditure burns energy when we sleep, eat, drive, and sit at our desk.

The real point I want to make is this: Our bodies are very finely tuned with respect to what they store.  What you eat matters a lot, but much less because of the actual caloric content of the food (there is probably not one of us who can titrate their daily intake to within 10 calories of a target intake).  The reason what you eat matters is because of the hormonal impact food exerts over your body.  The master hormone that regulates fat accumulation is insulin.  Hence, the impact your food has on insulin levels is far more important than the number of calories contained within what you eat.

So next time someone tells you, “you are what you eat”, feel free to correct them: You are not what you eat, You are only that small fraction of what you eat that your body chooses to save.  What you eat impacts this more than anything else.

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About the Author:

Peter Attia, M.D., is a physician in private practice in NYC and CA. His practice focuses on longevity and healthspan. His clinical interests are nutrition, lipidology, endocrinology, and a few other cool things.

Discussion

  1. Sandra Reese  December 14, 2011

    Enlightening! Wow!

    (reply)
  2. Elenor  January 25, 2012

    Where’s your archive? I’ve come over from Gary Taubes’ blog — and I can’t find a list of blog entries — or any way at all, really — except to randomly catch links in your entries, to read more. Your ‘recent posts’ are the same on every page — so where are the rest?

    Most blogs have a month-by-month archive you can reach from any page. I want to read more of your entries — so help me out, please!

    (reply)
    • Peter Attia  January 25, 2012

      Ah, Elenor, you’ve exposed me…I used to have an archive section until a week ago when something screwed it up. I’m working on a fix, so please by patient. For now, you can scroll through most of my entries on the main page (page after page, meaning go to the next page when you get to the bottom of one page). Will work on a fix as soon as possible. UPDATE: it’s fixed, thanks to Morgan Mallory. It’s called “Past Entries.”

    • Elenor  February 26, 2012

      YAY! Thanks! Very much enjoying your blog — and your friendship with my hero Gary Taubes adds to the pleasure!

  3. Marilyn  January 31, 2012

    Welcome. Wishing you and Gary Taubes well with your new project.

    (reply)
    • Peter Attia  January 31, 2012

      Thanks so much. The fun is just starting…

  4. LalBeral  February 8, 2012

    I’m looking forward to reading more on your blog. Gary Taubes’ books were so revelatory for me, and I’ve been eating very low carb (under 20g of carbs a day) for about a year, with occasional cheats. I don’t have much more to lose, maybe only 5-10 lbs., but that last bit doesn’t want to come off. I’m a 41 year-old fairly active woman.

    I’ve been avidly reading some of the paleo diet books and blogs out there (Eades, Sisson, etc.) and I’m left with some confusion about total calories. I also read on one of your posts that you have problems if you let protein go too high.

    So, I’d like your opinion: How much do calories matter really? At all? They don’t seem to for you! Or is it just a question of carbs (and to a lesser extent, protein)? If I eliminate carbs and keep protein under control but eat fat when I’m hungry, even if that adds to calories, should that affect weight loss?

    Also, what do you think about coffee? Since I need an “addiction” (living without sugar or starch), I’ve turned to drinking about 3 8-oz. coffees a day, black. Thanks for your insights!

    (reply)
    • Peter Attia  February 8, 2012

      Thanks so much for your questions and comments. I actually have a post already written on this question of “do calories matter.” Hope to get it out in the next month or so. On the coffee thing, I love it. Love the smell, love the taste, and love it unsweetened, but with with whole fat cream. If anything, the data suggest caffeine can actually increase mobilization of fat, by upregulating hormone sensitive lipase (HSL).

  5. Anthony  February 8, 2012

    Dr Peter.
    I never considered calories over the course of a year. We have been so conditioned to monitoring calories over a 24 hour period. It is almost hard to imagine that ONLY 10 calories per day is responsible for long term weight gain as you demonstated. Like you I love my coffee – it is my one and only vice. But mine is a cappuccino, large one – obviously made with full cream milk. Where do you sit with milk? The hardcore primitives don’t do it, some say its okay in moderation, but I suspect my current daily dose might not be the best thing to getting me to my end weight goal.
    To date – lost 19 lbs (in 9 weeks). Goal loss is 30 lbs. All done without sugar or grains.

    (reply)
    • Peter Attia  February 8, 2012

      Anthony, great question. I, personally, do not consume milk, as even one glass takes me out of ketosis, as I’ve documented in myself. My way around this: If I get a latte, I ask them to make it will whole fat cream (35% fat). Yes, they look at me like I’m crazy, but it tastes like nothing I’ve ever had and it does not appear to adversely impact me.

  6. Vlada  October 2, 2013

    As for Anthony, my only vice is coffee with milk. Now, when I am on this diet, I don’t know what kind of milk/cream I should use? In my country, we don’t have something called “heavy cream”, there is only milk, highest 3.8% of fat and something what we call “sour cream”, with 36% of milk fat. So, can you please be kind and just write nutrition information for that heavy cream that you use, and of course, is it made from milk or other ingredient?

    Thank in advance 🙂

    (reply)
    • Mihir  October 8, 2013

      here is the nutrition information for the heavy cream I use. :

      Ingredients
      Organic Grade A Cream (Milk)
      (Cream is the thick, fat-rich part of milk, which rises to the top when milk is fresh and is skimmed off.)

      Nutrition Facts
      Serving Size 1 tbsp (15ml)
      Calories from Fat 50
      Calories 50

      % Daily Values*
      Total Fat 6g 9%
      Saturated Fat 3.5g 18%
      Trans Fat 0g
      Cholesterol 20mg 7%
      Sodium 5mg 0%
      Total Carbohydrate 0g 0%
      Dietary Fiber 0g 0%
      Sugars 0g
      Protein 0g

  7. Rob  January 16, 2014

    Peter, I’m new to the site and deeply impressed with it your personal journey, commitment, and story. A lightly ketogenic diet is having a profoundly positive impact on my own journey to overcome a lifetime of weight management issues. And as you’ve mentioned, finding a PCP that supports my fairly well-read intention to pursue this form of insulin regulation, has lead me to make a change there. That said, this may not be the place to pose this question, so please forgive that, but, here goes:

    It seems from all the studies and interventions I’ve read that there is an underlying presumption that virtually everything we consume is processed by the body (except for some cellulose/lignin fibrous matter), and nothing is left. This leads me to conclude that fecal matter, other than water and the above insolubles, contains very little in the way of caloric materials, and certainly nothing that could be catabolized by the body’s native abilities. After subtracting the water, there must be left a certain amount of organic matter of some form (micro-organisms or parts thereof?). Is it correct to assume that everything that could be consumed is actually consumed through the alimentary canal and that virtually zero energy is lost in waste? And following that and the theme of this post, maybe it would be nearly correct to say “you are what you eat, and you are EVERYTHING that you eat.”?

    (reply)
  8. Kevin  June 10, 2014

    Peter, I have often wondered about feces (don’t laugh!)

    Okay, now that you’re done laughing, I was wondering about how much of what we eat never does get absorbed. I’m sure it would depend on a number of factors, but how much of our food ends up in the commode? When I see pieces of almonds in my stool, I know that there’s some fat and protein that didn’t get absorbed.

    Also, when our bodies secrete bile salts from the gall bladder to emulsify the fat in my low-carb/high-fat diet, and then is bound by the fiber I eat along with it, those high-cholesterol bile salts are then eliminated, rather than being reabsorbed (which is why high-fiber diets reduce cholesterol). Wouldn’t that count as a net-negative on energy?

    (reply)
    • Peter Attia  June 11, 2014

      Yes.

    • Hemming  June 19, 2014

      Does that mean that something like cocoa nibs, which are almost all fibre, would actually have a lower caloric value than what can be calculated? They have around 50g of fat per 100g but does the fibre affect the digestion so that I effectively can only use an amount less than the 50g as actual energy?

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