This is a two-part video that contains Dr. McGuff’s presentation of some of the key points of Chapter 9 of Body By Science. This is an excellent summary of the actual science underlying how human beings lose body fat and the role of high-intensity exercise in optimizing the fat loss process. Here are the links:

The Science Of Fat Loss (Part 1):

The Science Of Fat Loss (Part 2):

— John Little


  1. I noticed I made a mistatement. I stated that hormone sensitive lipase (HSL) mobilized glucose. HSL actually mobilizes fatty acids from the adipocyte. It is the glycogen phosphorylase enzymes that mobilize glucose. What is correct is that both of these enzymes are triggered by adrenaline during high intensity exercise and have amplified effects through an amplification cascade.

    Doug McGuff

  2. Dr. McGuff:

    You make a good case that there is much more to fat loss than just the simplistic thermodynamics arguements that most fitness folks make. But in absence of a caloric deficit, how are excess macronutrients, fat for example, expelled or otherwise escorted out of the body? We don’t start expelling glucose into the urine intil cbg readings of 600 or more are reached, and at that point, a paunchy belly is the least of your problems. Even in the correct hormonal environment, isn’t a deficit still necessary?

    Does the correct hormonal environment require a smaller deficit for fat loss than does an insulin resistant environment and can this be quantified? Can the correct hormonal environment actually produce fat loss even in a mild caloric surplus?

    As a chubby, 44 year old ER nurse, I’m curious. What happens to excess calories in a more proper hormonal environment?

  3. Can you point me to studies that support the hormonal theory you’re laying out, especially ones where calories are controlled?

    I ask because I have a hard time imagining that anyone switching to mostly meat, veggies and fruit would not also be reducing calories.

    And what if one doesn’t like meat? I never have, and haven’t eaten red meat or fowl in over 30 years… I’ll have fish once a week.

    Also, you’re suggesting that the hormonal effect (with amplification) of once-a-week weight training is enough to result in significant fat loss?

    I’d love to see studies demonstrating this, too.


  4. Steven,

    When you get the book, all the chapters are referenced. Also, for much greater detail than I could ever provide, I suggest “Good Calories/Bad Calories” by Gary Taubes. It will answer all of your questions and more. Also, see my comments on the post above this one.

    Doug McGuff

  5. I’m looking forward to the book. Having just read Gina Kolata’s “Rethinking Thin,” I wonder how much of what you describe is influenced by genetic factors. Billy Blank from Tae Bo has genetics that make him look like, well, Billy Blank… but doesn’t that suggest we each have genetics that make us look like, well, us?

    Among other things, Kolata describes studies that show the genetic influence by demonstrating the individual variation in weight/fat/muscle gain that occurs when people are equally overfed (e.g. a caloric overload that should result in a 23 pound weight gain resulted in gains of 9-29 pounds, depending on whether the subject, due to genetic variations, converted more of the excess calories to lean muscle or fat).

    Similarly, she recounts the extremely convincing studies that show the genetic influence of our bodyweight (and composition) set point.

    I’m also remembering hospital studies where macronutrient ratios were highly controlled and where the only factor that influenced weight loss was caloric input… but, clearly, these people weren’t doing any high intensity lifting that might have switched on some other metabolic activity.

    When I think about individual variation, I remember that I was always at my leanest when I ate predominantly carbs and very little protein and doing a lot of high intensity activity (gymnastics, bike racing, sprinting, etc.).

  6. Oh, and let me add that I recently had some genetic testing done (by 3 different companies). Each of them said, “You have a genetic variation that makes you prone to high cholesterol.”

    And, even though I’ve been an athlete most of my life, and rarely eat animal products, my cholesterol is borderline high. Even when I did eat meat, same thing.

    So, again, I’m curious about individual variation in what you’re describing.

    And, FWIW, Taubes’ book and ideas have been criticized with quite credible supporting evidence. Again, looking forward to seeing the studies you reference.


  7. Steven,

    Genetics will influence individual responses. Calories do count, but they are a DEPENDENT variable. Dependent on type of food that make up the calories, types of activity and hormonal environment that results. Set point seems evident on first blush. My experience is there is no set point that is fixed. Once metabolism becomes deranged, there is NO negative feedback loop to regulate a set point. The morbidly obese are ravenously hungry and will gain weight ad-infinitum.

    Doug McGuff

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