October 17, 2022

Body Composition

#227 – AMA #40: Body composition, protein, time-restricted feeding, fasting, DEXA scans, and more

“We don't want to be consuming protein for energy purposes at all. We want to be consuming protein for muscle protein synthesis.” —Peter Attia

Read Time 30 minutes

In this “Ask Me Anything” (AMA) episode, Peter discusses the importance of understanding body composition and explains how to interpret the most important metrics revealed by a DEXA scan, such as lean muscle tissue mass, visceral adiposity tissue mass, bone mineral density, and more. He discusses common concerning trends in these metrics as well as strategies to address them. He goes through DEXA scan results of both male and female patient case studies and explains the prescribed intervention for each patient. Additionally, Peter answers numerous questions about dietary protein including how much we need, when we need it, and how intake should be divided throughout the day to optimize muscle protein synthesis. Finally, Peter provides his updated point of view on time-restricted feeding and fasting and how his personal approach and recommendations for patients has evolved.

If you’re not a subscriber and listening on a podcast player, you’ll only be able to hear a preview of the AMA. If you’re a subscriber, you can now listen to this full episode on your private RSS feed or on our website at the AMA #40 show notes page. If you are not a subscriber, you can learn more about the subscriber benefits here.

We discuss:

  • Interpreting DEXA scans: important metrics, radiation levels, and more [2:15];
  • DEXA metrics: Bone mineral density (BMD) [12:00];
  • DEXA metrics: Visceral adipose tissue (VAT) [14:30];
  • DEXA metrics on lean tissue: appendicular lean mass index (ALMI) and fat-free mass index (FFMI) [20:45];
  • Concerning trends in BMD, VAT, & muscle mass revealed through DEXA scans [24:15];
  • Muscle and lean tissue loss with age and how to overcome anabolic resistance [29:15];
  • Female patient case studies: DEXA scan results and prescribed interventions [35:00];
  • Male patient case studies: DEXA scan results and prescribed interventions [42:45];
  • Protein consumption: recommended daily intake, Peter’s personal approach, timing around workouts, and more [48:15];
  • What to look for with protein supplements [53:15];
  • Protein intake: optimal timing and how it should be divided throughout the day [55:30];
  • Time-restricted feeding (TRF): Peter’s updated perspective [57:45];
  • Three strategies for reducing energy intake in over-nourished patients [1:03:15];
  • Prolonged fasting: potential benefits and tradeoffs [1:07:15];
  • A protein-supplemented version of time-restricted feeding (TRF) [1:09:30];
  • Theories about time-restricted feeding (TRF) and its positive influence on sleep and circadian rhythm [1:12:00]; and
  • More.


Interpreting DEXA scans: important metrics, radiation levels, and more [2:15]

What is a DEXA scan?

  • DEXA scan is sort of a moving X-ray
  • You lay on a table and get a really low-powered X-ray—meaning very little ionizing radiation
  • There’s a plate behind the object or the person being X-rayed, and it’s effectively looking at what’s hitting the plate
  • The more dense something is in front of the plate, the less electrons that are going to hit the back of the plate

Is radiation a concern?

  • There’s a unit in radiation that we talk about, and it’s usually millisieverts of radiation, and the more radiation to some extent is harmful
  • So the U.S. Nuclear Regulatory Commission (NRC) recommends that a person receive no more of 50 millisieverts in a year,
  • To put that in context, just living at sea level is something to the tune of one to two millisieverts per year—maybe 4% of your annual allotment
    • So if you lived in Colorado, where you’re basically a mile above sea level, it’s about twice that amount that you’re getting
  • If you look at something like an East Coast to West Coast flight — it would be about 40 microsieverts
  • And again, a microsievert is 1/1000th of a millisievert
  • A mammogram would be about 400 microsieverts or a 0.4 millisieverts
  • Chest X-ray, depending on the size of the individual, maybe 25 to 50 microsieverts
  • Conversely, a CT scan of the chest, abdomen, and pelvis could be up to 20 millisieverts, which would be about 40% of your annual allotment
  • All that just to put DEXA in context because it is a virtually radiation-free technology comparatively—it’s typically less than 20 microsieverts
  • So a DEXA has no more radiation than even the lowest end of a chest X-ray
    • It has 1/20th of the radiation of a mammogram
    • And it has about half the radiation of a cross-country flight

How often should someone do a DEXA scan? ⇒ This is a type of scan that you would do once, maybe twice per year

What is DEXA looking at?

  • It has the capacity to distinguish effectively three things: i) bone ii) fat, and iii) other
  • Those are basically the three buckets that DEXA is distinguishing based on the density of what the electrons are going through

DEXA gives you four broad pieces of information

1 – Body fat 

  • calculated in two ways, but probably the best way to do it is to take the total amount of fat and divide it by the total mass of the individual. And that gives you percent body fat
  • Technically, you can subtract out bone mass when you do that and get tissue fat percent. And by the way, that doesn’t differ very much because bones don’t weigh that much, just in case you’re wondering where that discrepancy can be.

2 – BMD, bone mineral density

  • That is both reported in an absolute amount in grams centimeter squared
  • And it’s also reported in a z-score
  • ⇒ Check out the previous AMA on bone health

3 – An estimate of VAT or visceral adipose tissue

  • It’s just an estimate based on looking at the amount of fat that is in the torso, above the anterior superior iliac crest, and the ribs, and kind of trying to subtract out what it believes is in the subcutaneous space, and therefore looking at the difference
  • visceral fat is a relatively small fraction of total body fat, but it’s important to get that right because it’s so much more indicative of risk

4 – Appendicular lean mass index (ALMI) and fat-free mass index (FFMI)

  • Sometimes it does this directly, it just tells you the appendicular lean mass index, but sometimes you just have to calculate it
  • And you can always calculate the fat-free mass index, both of which we’ll talk about
  • These are measures of how much lean mass you have or muscle mass in the extremities
  • This is always reported as total amount of lean tissue divided by height in kilograms per meter squared 
  • Both appendicular lean mass index and fat-free mass index, which is just total mass that is not fat, divided by height in kilograms per meter squared 
  • They’re both reported therefore in kilograms per meter squared


  • You essentially get those four things from DEXA and you want to see how you stack up against a population
  • The population is typically stratified by your sex and by your age, therefore, we have nomograms for each of these things,
  • And that’s how we present the data to a patient and that’s how we therefore make decisions about where you rank and what you need to do

*Point of clarification when choosing a place to get a DEXA scan:

  • Not every place you get a DEXA scan will give you those exact metrics (BMD, VAT, ALMI and FFMI), but every place will provide the metrics you need to come to the conclusion of that for yourself
  • There is one important exception: 
    • There are some DEXA places that only give total body z-score for bone, and they don’t break it out individually by hip and lumbar spine
    • You can’t make a diagnosis of osteopenia or osteoporosis, or frankly assess BMD clinically without that feature
    • In other words, if you just look at total body BMD, the z-score for the total body is too easy to mask what’s going on in those areas
    • So if there’s any concern about BMD, you’re going to have to go to a place that is able to give the segmented information


DEXA metrics: Bone mineral density (BMD) [12:00]

Overview of BMD

{end of show notes preview}

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  1. I follow Dr Attia on twitter, instagram and this newsletter. I also read most of the transcripts of The Drive and I am catching up on the QALYs.
    It comes as a shock to me to learn that Peter has stopped doing 3 days fast for 18 months. I feel like it was not that long ago that he was saying that fasting was one of the greatest possible tool we have for autophagy and health (on the level of exercise). For example the Eileen White episode.
    Was this change of stance discussed somewhere before? Did I miss something?

  2. Love the case study portion of this AMA. What would be interesting in another AMA is to compare these Case Study Dexa scans (the initial/baseline scans) and compare them with Dexa scans after these patients have applied the plan for them to improve these metrics. Love listening to these podcasts. I share this information with my students(I am an Anatomy and Physiology Professor) and my husband who is rural health care family doc.

    • Kathy, I am also an A&P and nutrition professor and also carefully use Dr. Attia’s information with my students. Good to know I’m not the only one!

  3. I’m a new subscriber and loved this podcast! It happened to come on while driving to my monthly Dexa scan.
    I figured my ALMI when I got home–8.45 as 48yo F That’s in the high 90’s percentile, and BMD is also quite high. Despite losing 60lbs primarily through TRE, my BF% is 36. So, still quite obese.

    According to the podcast, that combination means LOSE FAT, worry less about lean mass preservation.

    My favorite tool for losing fat is Alternate Day Fasting, i.e. a 36:12 fast. As a former scientist, I like to do 30 day body composition experiments, and compare the results of one strategy over another using Dexa.

    I agree with a lot of what you mentioned about TRE in this podcast, and yet in the online discussion forums of the masses–it seems to be a profoundly successful tool for long term weight loss compared to other methods. I have not seen any studies that attempt to quantify the real magic of moderate TRE. You eat less, because you metabolically feel like eating less, without feeling restricted by a bogeyman. None of the isocaloric studies allow for ad libitum eating in the TRE arm, which is the magical essence of TRE. I’ve often argued that TRE plus “medicinal salmon” taken during the fasting window to combat any lingering hunger is a great tool.

    Here’s my question.
    I’d like to compare two strategies for lean mass retention and maximizing fat loss with my next two 30 days experiments. What would you do with this idea if you were me?

    My current thoughts are:
    Strategy one: Eating max protein targets, keeping glucose steady and cortisol low plus strength training without TRE.

    Strategy two: Low-ish carb ADF 36:12 and its inherent hGH with the same strength training and accepting protein “wasting” during the eating window, and potential for cortisol during fasting to rob lean mass to provide a substrate for gluconeogenesis.


    • I would go with one based on my experience, without TRE with a 300-400 Cal deficit and kept most of the lean tissue and strength training 4-5 days a week and did a DEXA after 1 yr . Body fat reduced and lean tissue kept the same.

    • There are some products on his page here: https://peterattiamd.com/members/discounts/

      My related question is: I’m lactose intolerant, and every whey product I’ve tried so far gives me GI distress, so I would be curious to know of any recommended alternatives for low-fat, low-sugar, complete dairy-free protein. I like the Clif Builder bars for taste and protein composition, but they are too high in fat and sugar to work while I’m trying to cut.

  4. Just had a DEXA scan on Friday – was very helpful to go through my results real time today during the show. 58 y/o male, 21% body fat, 38 lb of fat mass with 448g VAT mass.

    Results say 4% total body percentile for age but ALM is only 55% for age. Doesn’t seem consistent – thoughts on why?

    Is there anything special to do (diet, strength/cardio, etc.) to target visceral fat reduction? Or is it lost proportionally along with overall fat?

  5. I am curious what your thoughts on this Stuart Phillips (@mackinprof) thread:
    “The overall effect of protein intake on gains in lean body mass and strength is tiny. On an individual level, I’d go so far as to say they are non-existent or at least non-measurable. The effect sizes even with very large sample sizes are unimpressive…”
    “Minimum 1.2 g/kg/d, benefit to 1.6 g/kg/d. After that, I don’t see any evidence for benefit.”
    Finally, in a reply someone suggested potassium had greater effect citing: https://nutritionj.biomedcentral.com/articles/10.1186/s12937-020-00614-z#Sec9
    “In men, higher potassium intake was associated with lower odds for low muscle mass; the fully adjusted odds ratios (95% confidence intervals) were 0.78 (0.60–1.03), 0.71 (0.54–0.93), 0.68 (0.51–0.90), and 0.71 (0.51–0.98) for the top four quintiles (referenced against the lowest quintile), respectively.”

    Do you find the study @mackinprof cited convincing? Is potassium more important than protein?

  6. Two comments:
    1) As mentioned in the podcast, a DEXA scan is a low energy x-ray. (It’s actually dual energy x-ray for a very good reason but that is a technical detail.) In the podcast, the x-ray was referred to a being comprised of electrons. X-rays are photons, not electrons.
    2) As you say in the show notes, ALMI and FMI are reported in units of mass over length-squared. But the language is confusing & imprecise while it gives the impression of the opposite: “This is always reported as total amount of lean tissue divided by height and meter squared”. Similar language is used in the podcast. The formula is ALMA or FMI = mass / (height*height), where mass is in kg and height is in meters. You don’t divide mass by “height and meter squared”.

    • Another very helpful podcast. I’ve been a member for years and just started looking at the show notes, they’re a huge help.

      I noticed the same thing in the notes. It almost looks like a speech-to-text error. In this particular podcast Peter makes several obvious slips, (normal for anyone in 90 minutes of discussion) but it’d be good if Nick could correct them in real time, which he does occasionally. Just as another example, in the discussion in Figure 4 and in the podcast, Peter says fat mass drops off a cliff at age 75. What he means (which was obvious from the context) is that fat free mass drops.

    • I saw this too and was confused. My DEXAs are in pounds and inches so I assume I need to convert to kg and meters then calculate ALMI.

  7. Super helpful, Thank you. This AMA dropped on the day, I went for my first DEXA and VO2 Max test at Samford University. Now I have a ton of information and a framework to understand how to synthesize my results and choose an approach for my under-muscled, over-nourished Dad bod!

  8. Hi — this is great. I just had my first DXA and have two questions.

    1) how do I calculate my AMLI? I got my results in pounds, and understand I need to add arm muscle mass to leg muscle mass, but am not quite sure how to setup the numerator and denominator based on the transcript, and don’t see a calculator or guide in the show notes.

    2) based on my results, I have great bone density (97th), adequate total body fat percentage (50th), but concerning VAT (97th). Not a surprise given family metabolic history. Question: do you think about VAT as being symptom or cause or both? Are there strategies for targeting VAT reduction specifically, or is it an eventual byproduct of general fat loss? Little unclear on the latter given your statements about being surprised by different compositions.

    Love the podcast.

  9. Peter, later in the podcast you gave the goal of 1.6-2g of protein per *pound* of body mass in non-obese individuals. Did you mean per kg? Because when you described your own goal of 180g, I am assuming you are not 90lbs…just want to make sure.

      • Thanks Nick! Appreciate all the work you do with these resources — I was reading the show notes while listening to the podcast in between deadlift sets at the gym 🙂

  10. I am glad to see that Peter has a very open mind about evolving ideas. His progression of views on fasting is remarkable.

    I remember this quote from an earlier episode: “In fasting we have arguably the most potent tool, and certainly if not the most potent, probably one of the three most potent tools, in which we can affect human health, and we don’t have a clue how to dose it or what frequency with which to use it. And I find that ridiculous.” —Peter Attia

    I know that he somewhat discussed this in the “loosely held” AMAs, but I am curious, was there research or an event that prompted such a drastic change? Or is it strictly his desire to consume larger quantities of protein than TRF would allow?

    Also, will Peter stay on as an educator and investor in the Zero app, since this is no longer aligned with his teachings?

    Keep up the great work! As a fellow surgeon and “functional medicine doctor”(for lack of a better term), I appreciate the discussion and witnessing the evolution of medicine. Peter has pushed the ball along more than anyone.

  11. Great podcast on practical solutions. It would be nice if we have the Post DEXA results after these prescriptions to the patients . I find it hard to align my numbers with the DEXA Nomograms . These Nomograms doesnt show the exact values
    The division of numbers are not clear to me on those. Is there any where online we can put our numbers and see where we fall under ?

  12. I came here to check the notes on the proper protein ratio (thanks for correcting it before I attempted 400g a day!)… but I noticed a comment about different types of supplementation for people who have trouble with Whey… are there any cons to using pre-digested protein?

  13. Loved the episode. I’m lactose-intolerant (like, I imagine, many others). I’ve heard that non-dairy protein supplements are often missing particular amino acids and need to be combined. Would very much appreciate recommendations for non-whey-based protein supplements, and also for people limiting meat intake due to lyme-induced (alpha gal syndrome) issues. Thank you!

  14. You explanation and interpretation of DEXA scans was mavellous. Your dietary recommendations were disappointing at least and contradictory at best. Your proposed nutritional recommendation concerning high protein consumption for muscle mass was a times diametrically opposed to the clinical and scientific research conducted and discussed with scientists in your previous podcasts on health span and longevity. I believe your scientific guests understand that muscle mass does not significantly decrease during intermittent und prolonged fasting. To make this AMA a discussion and not just a monologue, it would be a joy for the listener to hear the opinions of your other guests. For example: if you want to propagate high protein consumption for muscle mass, then you might want to discuss why low protein consumption and/or water fasting does not reduce muscle mass in metabolic diseased patients (Typ II diabetes, metabolic syndrome etc.) as your guests report on your show. Metabolic diseased patients do not require high protein diets as you prescribe for yourself. So why would normal metabolic healthy subjects require high protein to obtain muscle? Why not just say muscle mass comes from exercise, and leave it at that proven truth. Your monologue about your protein requirement just didn’t make any sense to me.

  15. Could someone please tell me if there are ever replies to these comments?? I see a several questions and wanted to ask one of my own but not seeing any response from the team?

    • Jennifer it looks like you can only reply or make comments on the most recent podcast listed, and none of the prior ones. So given how few people are going to go to the bottom of the show notes and look at the questions it’s highly unlikely any questions or comments here will be replied to by anyone in the vast majority of cases.

  16. Such an informative AMA episode. I have 4 DEXAs to look back at and will start tracking ALMI as well. Focusing on protein intake and heavy strength will hopefully help me maintain/ gain muscle at my post menopausal age.

  17. Has Peter spoken about pros and cons of getting protein intake strictly through plant-based diet? Is it even possible?

    • Yes Christina he has referenced in other podcasts the idea of vegan and vegetarian diets and related macros. In general the quality of the protein will not be as high but it’s doable (not ideal) with proper planning.

  18. I’m surprised that the VAT nomographs aren’t normalized for height. I’m 6’5” and apparently I need to aim for the same VAT target as someone much shorter.

  19. Does anyone recall the details on Peter talking about his own experience around 2013? I recall him saying he reduced his body fat over a number of years from when he was at his heaviest and then he took years to put on the muscle again. I’m asking as I’ve just had a DEXA and I’m 50th percentile ALMI, very low VAT and 50% body fat. I’m assuming the order is, increase ALMI first then bring body fat down second? They may happen together but its much easier to target the diet if I have a primary goal in mind.

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