Digging into the Bodyrecomposition Mailbag

Since I can’t think of any actual topic this week and think I can answer these questions in a fairly brief manner, I’m just going to clear out some of my questions.  Topics will include women and DEXA, oddities about pregnancy metabolism, endurance nutrition and a bit about health habits when you have bipolar.

Question: Hi Lyle, I recently did a DEXA scan to get an estimate of my body fat % – I’m female, 28 years old, weight train regularly. My DEXA scan results: 5’3, weighing 59kg and an ‘average’ of 20% body fat. I say ‘average’ as the scan showed that the body fat % in my upper body (arms, torso) was 14% while my lower body (hips, thighs) was 27%. Is it fair for me to take the average of these and consider myself to be 20% body fat?

Answer: The above type of question is becoming more and more frequent as more people are using DEXA scans to get an estimate of bodyfat percentage (BF%).   Because of the way DEXA works, it will churn out different BF% for the upper and lower body and this can be confusing.  First and foremost, the above is a completely normal female body fat patterning as women generally carry more body fat in the lower body than upper body (a male would typically have the opposite pattern).  I say generally as there can be exceptions where women have either a very even body fat pattern or more of a male-like upper body fat patterning; the latter typically occurs in situations were testosterone is above normal.  So far as the main question, should the values be averaged to get a usable BF%? The answer is yes.  In any of my books and most discussions of applications of BF%, it’s whole-body BF% that is relevant, not the individual distributions.

Question: I was wondering if you could make sense of this article in terms of what you know about human metabolism:

Answer: The paper in question deals with the issue of resting metabolic rate (RMR) and it’s determinants.  Normally, the largest determinant of RMR is lean body mass (LBM).  Here I’m talking about all LBM, not just muscle.  Organs, brain, etc. actually burn far more calories per day than muscle and LBM predicts a majority (off the top of my head: 75% or so) of RMR.  But this study found that in pregnant women, it was the amount of body fat that predicted RMR, concluding that:


Anxiety Low-Carbohydrates Whey and BCAA

Question: Hi Lyle. I happened upon your site while researching the connection of dieting leading to anxiety. I am prone to anxiety and panic attacks and have been on zoloft 50mg for years. As of mid November I did Isagenix 30 day program with one day a week of a cleanse. The cleanse days were horrible for me as I don’t do well on not eating. Anywhoo…after I completed the month of cutting out a lot of carbs and drinking their whey protein shakes 1-2x a day, drinking BCAA’s and eating healthy, I had a major panic attack about a week and a half later. It was odd. I hadn’t had one in years. I am very active.

I teach Cycle, Boot Camp and am a long distance runner. I workout 5-7 days a week. This panic attack was about 4 weeks ago. Since then, I have had to increase the Zoloft to 75mg and I’m trying to get through the upstart side effects (ironically, agitation and anxiety increased) that I can’t seem to shake just yet (4-6 weeks to feel a difference. I am on week 3). I just wanted to get your opinion on the correlation between dieting and anxiety. I am curious if the addition of adding Whey protein with amino acids and BCAA’s once / twice a day caused this issue. I am SO frustrated to not feel normal again and it has definitely hindered my outlet – running. Thoughts would be greatly appreciated! Thanks!

Answer: Ok, I swear this will be a short one.   I addressed this a lot of this within the context of depression as well and you can go read that for most of what you need to know.  Tangentially, re-reading that piece, I couldn’t honestly write it today.  I suspect I was mired in a bunch of research on the topic because most of those details are completely wiped from my brain.  In any case, reading that will give at least some background to this question along with some general concepts of how to address it.

Now, first let me state that anxiety spans a lot of different types of things; interestingly, and suggesting that serotonin plays a role in many of them is the fact that Selective Serotonin Reuptake Inhitibors (SSRI’s), drugs that raise serotonin in the nerve space by preventing it’s re-uptake appear to have major benefit for treatment of anxietyZoloft which you mentioned being on is an SSRI (and note that SSRI’s take 3-4 weeks to really kick in for some reason). As well you didn’t mention if you’re still on a low-carbohydrate diet.


Carbohydrate Loading for Endurance Events – Q&A

Question: Lyle, what does the science say regarding the proper protocol for carbohydrate loading before a goal endurance event like a full marathon? As usual, internet articles are all over the place: some say 2 days, some a week or more, some say keep calories the same but higher carb percentage, some say to jack it up to 5-7 g/lb…Appreciate any advice! PS – if the answer is “it depends”, please pretend the individual is running 50-60 miles per week with a goal of qualifying for Boston.

Answer: Since I’m at a bit of a loss as to what to write about today, I thought I’d get into the mailbag and take what will be a fairly quick and easy one: carbohydrate loading.  As usual, I’ll give too much background instead of getting to the point quickly.

What is Carbohydrate Loading?

The concept of carbohydrate loading is fairly simple.  First and foremost it’s based on the fact that during fairly intense exercise, fat cannot contribute as much to energy production as most would like (folks spent decades trying to improve this but the fact is that near threshold intensities, carbohydrates are the primary fuel source).

At best fat adaptation increased the body’s ability to use fat for fuel at lower intensities, sparing muscle glycogen but it also came with some problems, including the impairment of the use of carbs for fuel (due to some enzymatic changes) during sprint performance.  Since real sports have bursts and sprints (in contrast to studies which often use submaximal time to exhaustion), this is relevant.

In any case, the concept of carbohydrate loading is that through some types of dietary manipulations, the body’s normal glycogen stores (glycogen is carbohydrate stored in muscle and liver) can be overfilled, like overfilling the gas tank after the nozzle stops.  This puts more fuel into the tank.  So why is this useful?


Calories Not Matching Macros – Q&A

Question: This may come across as sounding like a very rookie question so bare with me. I just had a question regarding my macros/calories. My current macros are at 46 fat, 165 carb and 144 protein and calories at 1650. However, recently I have been hitting my macros spot on but not my calories. I am aware that there is 4 calories per gram of carb/protein and 9 calories per gram of fat. What am I doing wrong?

Answer: This is going to be a very short Q&A since I am currently embroiled (perhaps better described as overwhelmed) in the editing of the Women, Training and Fat Loss book.  Just in case anybody is not familiar with the term, macros is simply short for macronutrients and refers to protein, carbohydrates, fats and technically alcohol.  It’s all nutrients that are consumed in large amounts (lots of grams).  Fiber could technically fit here as well.

Calories are a measure of energy.  Technical one calorie is the amount of energy required to heat 1 gram of water by 1 degree Celsius.  This is done in something called a bomb calorimeter and many correctly point out that the human body is not a bomb calorimeter.  But this is all accounted for and yields the Atwater constants.

Nutrient Calories/g
Protein 4 cal/g
Carbohydrate 4 cal/g
Fat 9 cal/g
Alcohol 7 cal/g
Fiber 1.5-2 cal/g


Mixed Brain Fuel – Q&A

Question: On a ketogenic diet, how rapidly does the brain flip between glucose and ketones for fuel? Can it use both fuel sources simultaneously?

Answer: The above question sort of encompasses a few different potential things and I’m not 100% sure which you’re asking so I’ll just cover them all.  First realize that one fuel that the brain cannot use is fatty acids, at least not directly.  This has led to the oft-stated belief that the brain can only use glucose. But this is incorrect as the brain has an alternative fat derived fuel which are ketones (or ketone bodies, the two major of which are beta-hydroxybutyrate and acetyl-acetate).

Ketones are produced primarily in the liver (from the breakdown of fatty acids) and exist predominantly as an alternative fuel source for the brain (they can also be used by skeletal muscle) during periods of low-carbohydrate availability.  This probably was originally important during periods of complete starvation; now very low-carbohydrate diets (defined here as any diet containing less than 100 grams per day of carbohydrates) effectively ‘exploit’ this mechanism.

Now, on a carbohydrate based diet, the brain runs essentially on 100% glucose since ketones are generally not produced in significant amounts under those conditions (there are a couple of odd exceptions, one is following very long duration endurance exercise where a post-exercise ketosis can occur due to changes in fuel metabolism).  So what happens when you remove most or all carbohydrates from the diet?  Does the brain magically switch to using ketones?  For the most part, no.  Studies done way back when show that there is an adaptation phase that may last about 3 weeks while the brain ramps up its ability to use ketones for fuel.

Even there, after that roughly 3 week period, the brain still only derives about 75% of its total fuel requirements (about 400 calories per day or thereabouts) from ketones; the other 25% come from glucose (which the body can produce through a variety of pathways that I won’t detail here; all of this is explained in excruciating detail in my first book The Ketogenic Diet).  Mind you, this is only relevant on a very low-carbohydrate diet.  Even if the brain could still use ketones on a carb-based diet they wouldn’t be produced in large enough amounts for it to be relevant.