A review of Outlive, by Peter Attia, with a tl;dr at the end because it’s like 13 pages long

Peter Attia is the first person I would want to write a book on extending healthspan. Attia spent his undergraduate years studying to be an aerospace engineer before eventually going to medical school and entering private practice as a primary care doctor to the 1%, who pay him $150,000 a year to extend their lives. In his book, Outlive, Attia combines an engineer’s talent for optimization and quantitative analysis with a clinician’s pragmatism. While it does at times feel like it’s designed to promote his practice, Outlive is a genuinely useful book for those of us who can’t afford Attia’s rate.

As I read Outlive, I couldn’t help but think about David Sinclair’s successful 2019 book, Lifespan. In many ways, Attia and Sinclair have opposite views on longevity, and the two of them seem to know each other and talk, so it’s weird to me that neither of them appear to have publicly noticed that they disagree so strongly.

Sinclair takes a “candle” view of longevity: an oversimplification is that our bodies have a certain pool of metabolic resources and epigenetic fault-tolerance and that aging (well, technically senescence) is the exhaustion of this pool (burning down the candle). So Sinclair is careful to avoid “burning his candle at both ends” (a phrase he actually uses in his book), practicing both caloric restriction and fasting. He also has a lot of “longevity hacks” like sauna, cold exposure, and various drugs, which, as you’d expect from a researcher, he spends a good deal of time enthusing about in his book.

Attia, meanwhile, takes a “banking” view of longevity: the oversimplification here is that since nearly all physical abilities inevitably degrade over the long run, we need to put a lot of them in the bank to have a buffer for later. Attia wants to maintain high physical performance for as long as possible, so he advocates eating a gram of protein per pound of body weight every single day (for me, this would be like nine protein shakes). Obviously, this is combined with a very ambitious physical training program. Caloric restriction and fasting are discouraged in all but the most severe cases of metabolic dysfunction on the grounds that they will cause you to lose muscle mass. Sauna is briefly mentioned in the Alzheimer’s chapter, and a handful of drugs (a few statins and rapamycin) are mentioned by name but don’t receive much attention.

I genuinely don’t know to make of these radically different models and wish Attia and Sinclair would address them. One way to sum up this difference is that Attia expects physical decay due to aging to happen significantly faster than Sinclair does - which perhaps gives Sinclair a little more credibility. A lot of Attia’s stats in the book appear to come from averages without intervention, and when he looks at older people who are making some significant effort to improve, he often finds that they’re either holding off decline pretty effectively or even improving. This would suggest that we’re more likely than Attia acknowledges to get away with a more Sinclair-style approach. But since I don’t know much about medicine, my final analysis won’t rely much on this:

Sinclair, I assume, is ultimately chasing prestige, and getting mice to live slightly longer is his proxy for that. Based on the vibe from his book I suspect that Attia is also chasing prestige, but his proxy is something like positive feedback in his clinical practice over a 5-10 year time horizon. On the one hand, Attia has no reason to prefer any particular class of interventions over another (unlike Sinclair, who is incentivized to promote his own research). But on the other hand, we should expect that Attia will systematically undervalue very long-term approaches like Sinclair’s, because the candle theory probably produce worse results over any 5-10 year time horizon than the banking theory. Because of this, in absence of better information it makes a lot of sense to pay more attention to Outlive over the short term. If strong evidence supporting Sinclair comes out over the next decade (such as David Sinclair very persuasively continuing to look exactly the same as he did in the 1990’s), it might make sense to back off on some of Attia’s stuff. If not, you’re in a very good place.

So then, on to the book itself. Attia is concerned with two things: avoiding the most common causes of death and extending ability to perform everyday tasks. Like a good engineer, Attia continues to recursively break these down into manageable chunks, ultimately identifying four horsemen of death and five areas of intervention.

General Thoughts on Longevity

A reasonable question to ask about longevity before you start trying to make changes is whether anything can improve your longevity. There are obviously lots of things that can hurt (smoking, obesity, Russian roulette, etc), but can you really improve, or is your natural lifespan mostly genetically determined? Twin studies suggest that genetics only appears to be responsible for ~20-30% of variation in lifespan near the center of the distribution, but becomes a lot more important at the tails. In other words, it’s very difficult to become a centenarian without being related to one (and more bad news: if your family tends to die young, you probably will too). However, the good news is that, as I interpret it, most people can modify their lifespans by maybe 1.5ish standard deviations (maybe 15-20 years!). But just as importantly, we can die after a relatively rapid decline and spend most of our old age as independent, capable people rather than vegetables waiting to die.

Attia succumbs exactly once in this book to enthusiasm for an anti-aging drug and expresses a lot of optimism about rapamycin (commonly used as an immunosuppressant/immunomodulator to prevent rejection of donor organs after transplants), claiming that it’s one of the few drugs that has ever demonstrated the ability to improve lifespan but needs to be administered cyclically at high doses.

Horseman 1: Metabolic Disorders

Your blood glucose levels need to be kept incredibly stable, and this is partially the job of the liver, which must decide when to convert glycogen into glucose. But when you introduce a lot of glucose to your body, you have to store it, either as glycogen or fat. The job of insulin is to signal your cells to store excess glucose in your subcutaneous fat, which is actually healthy! One experiment transplanted extra subcutaneous fat into mice and cured their metabolic disorders because they now had extra space for their glucose. But if you don’t have enough space for all your glucose, your insulin levels start to have less impact on your blood glucose levels - you are becoming insulin resistant.

At this point you will start to see warning signs on a standard blood test: your fasting blood glucose will be high. If you’re not type 1 diabetic, your insulin levels have been elevated for the entire time you’ve been fasting, but you had nowhere to put your glucose and so it keeps circulating in your blood.

Your body wants to store energy as fat, and will do this even when it has to put fat where it’s not supposed to be: as triglycerides in your blood, in between your internal organs, and even on and within your organs, reducing their efficiency. Fat in these latter two locations is called “visceral fat,” and visceral fat is a very bad sign. Visceral fat in the liver causes fatty liver disease - if you have certain levels of this and you’re not an alcoholic, then you have a metabolic disorder called Non-Alcoholic Fatty Liver disease (NAFLD).

Note that everything we’ve said here points to the fact that weight, in and of itself, is not problematic! It is possible to be obese and metabolically healthy, and it is possible to be a normal weight and metabolically unhealthy. The metabolic health, not the weight, is the key.

How do we monitor for signs of metabolic dysfunction? Attia lists a number of ways:

While you might think of most of these as fancy tests for rich people, you can still get a rough idea of your metabolic health with just the standard blood tests from your doctor (which should include triglycerides, cholesterol, and fasting blood glucose).

Horseman 2: Atherosclerotic Cardiovascular Disease (ASCVD)

Your body needs cholesterol to survive, and it transports its cholesterol around in lipoproteins. A lipoprotein has a crunchy protein shell around a gooey cholerterol center, or so I like to imagine, and the the density of the lipoprotein is how much protein relative to fat (cholesterol) it has (HDL has more protein, LDL less). Lipoproteins aren’t water-soluble on their own, so they in turn are wrapped by apolipoproteins: HDL is wrapped by apoA, and LDL by apoB.

As they’re transported around by your blood, these apolipoproteins will occasionally become lodged in the endothelium which lines your veins. ApoA can easily pass through the endothelium and so is easily dislodged, but apoB will get stuck and oxidize, which leads to forming clumps. Your immune system and smooth muscle cells will both try to run damage control, possibly successfully, but sooner or later you’ll end up with an atherosclerotic plaque. If you run a CT angiogram, you can see these plaques, but a typical CT scan will miss them until they become calcified (basically your body trying to pour cement over the plaque to at least stabilize it).

But we don’t need a CT scan (which will show us damage already done) to make marginal health decisions: for this, we can simply measure our apoB, which we should do regularly as it’s an easy and relatively inexpensive test ($30 even if you have to pay out of pocket). You should start getting concerned at 70 mg/dL, but there is no minimum number for apoB - ideally, you drive it as close to zero as possible (though most likely you’ll end up somewhere around 20 if you’re very successful, and this is fine).

How do we lower apoB? One thing to point out is that dietary cholesterol doesn’t matter: humans synthesize their own cholesterol, and the cholesterol we eat is overwhelmingly just pooped back out. However, it appears that consumption of saturated fat can raise apoB for some people (though not for others). Attia typically has his patients make dietary changes (everyone should at least try reducing their saturated fat consumption), but he also puts almost all of his patients on statins, which improve clearance of LDL, and has them monitor their blood pressure (high blood pressure mechanically damages the endothelium and so creates more opportunities for plaques).

Attia also mentions Lp(a), an especially bad form of apoB which you may have a predisposition towards if premature heart disease runs in your family.

Horseman 3: Cancer

This chapter of the book mainly covers a number of experimental treatment and screening methods for cancer, such as immunotherapy and liquid biopsies. While this is certainly interesting, I’m afraid it somewhat plays into what I’ll jokingly call the Sinclair Trap of telling us about cool things we might see down the road instead of helping us live longer.

Attia’s approach to cancer is basically: we don’t really have many good ways to avoid cancer, and we’re not super great at treating it, so it’s very, very important to catch it early. Therefore, Attia recommends early and frequent screening for lung, breast, prostate, colorectal, and cervical cancer. Of these, my personal thought is that it makes sense for men to get PSA (prostate specific antigen) screenings and sigmoid colonoscopies early and often (full colonoscopies appear to have little effect on all-cause mortality). Women should get the colonoscopy, pap smear (cervical), and mammogram (breast).

Horseman 4: Alzheimer’s

You might have imagined from the length of the last section that cancer is the horseman we know the least about, but this isn’t true: we know virtually nothing about Alzeheimer’s. We don’t know what mechanisms produce its symptoms, we don’t know how you get it, and we don’t know anything about how to cure it. But there are a few insights that might be helpful.

One of the few things we know about Alzheimer’s is that a gene called APOE has a tremendous impact on whether you get it. You have two copies of APOE, each of which is either the e2, e3, or e4 variant. Most of the population has two copies of e3, which produces normal risk for Alzheimer’s, but if you have at least one e2 variant, you become less likely to get it, and if you have at least one e4 then you become more likely to get it. These are sort of dose-dependent, so an e4/e4 genotype is highly likely to get Alzheimer’s.

Beyond sleep and exercise (which will reduce your risk of having basically any problem, and are the highest-priority for Alzheimer’s prevention), we have two ways to prevent Alzheimer’s, and both are equally weird. The first is flossing: it seems that gingivitis significantly raises your odds of getting Alzheimer’s. The second is dry sauna. To quote Attia:

The best interpretation I can draw from the literature suggests that at least four sessions per week, of at least 20 minutes per session, at 179 degrees Fahrenheit or hotter seems to be the sweet spot to reduce the risk of Alzheimer’s by about 65% (and risk of ASCVD by 50%).

Those are, um, huge effect sizes, wow.

Intervention 1: Exercise

Attia identifies five areas of intervention in his book: exercise, sleep, nutrition, emotional health, and drugs. Of those, I will only focus on exercise and nutrition, because Attia doesn’t talk about drugs in this book, except for statins, and his thoughts on sleep and emotional health are pretty standard fare.

Attia believes that exercise is the most important domain in which you can intervene to improve your healthspan. He subdivides physical health/training targets into endurance, aerobic capacity, strength, and stability, and introduces the very interesting idea of the Centenarian Decathlon. Basically, Attia thinks that we should be exercising with goals in mind for when we’re in our 90s (or maybe older!). If you look at the typical decay curves in physical capabilities as people age, it turns out that you need to be quite fit in your 50s if you want to be functional and independent in your 90s. If you want to be able to pick up your grandchild, go for a hike, or carry your groceries up the stairs in a reasonable amount of time in your 90s, you may need to be performing near the level of exceptional athletes in your 50s (note: this is subject to my earlier note about Attia using average decay curves). Fortunately, Attia thinks this is an attainable goal.

Endurance

Aerobic endurance is the base on which all other exercise is built. This is where we reverse our metabolic problems and start the journey to performing at higher levels. In fact, even elite athletes (depending on their sport) might spend most of their time training in zone 2, which is where we’ll be spending our time.

Zone 2 is technically 70-85% of your maximum heart rate, but Attia suggests that we use our perceived exertion: we’re looking to feel that we can just barely hold a conversation. If you would struggle to speak a full sentence out loud, you’ve overshot; if you could easily sing, you’re not there yet. Attia himself does four 1-hour zone 2 workouts every week, and he thinks three hours a week is the minimum if you want to improve.

If you’re looking for a number to improve here, you want to see your body’s metabolism getting more efficient by producing a greater wattage per kilogram of weight. Oftentimes stationary bikes will show you your output as a wattage. Elite athletes tend to perform at around 4 watts/kg - metabolically unhealthy people are around 1 watt/kg.

Aerobic Capacity (VO2 Max)

A smoker has about a hazard ratio of about 1.4x relative to a nonsmoker, but someone in the bottom quartile for VO2 max has a 4x greater chance of dying at any given moment relative to someone in the top quartile. Even just exiting the bottom quartile cuts your risk by 50%. So improving aerobic capacity is literally vital. To quote Attia: “to be able to climb up four flights of stairs in your eighties, you should be able to pretty much sprint up those same stairs [in your forties].” Your aerobic capacity is measured by your VO2 max, which is the maximum rate at which your body can consume oxygen. After you reach the age of 50, VO2 max declines at a rate of roughly 10% per decade on average, and once it reaches 15-18 ml/kg/min it begins to threaten your ability to live on your own.

However, aerobic capacity is quite trainable even in older people, who might expect to see 17% improvement over the course of a year. Attia doesn’t start his patients on aerobic training until they’ve done 6 months of endurance work, and his VO2 max workouts are similar to HIIT, but “a bit longer… and a notch less intense.” They typically follow a 4-4-4 pattern: 4 minutes on (at the maximum intensity you can sustain for 4 minutes), 4 minutes off (at a low but nonzero intensity - should be enough for your heart rate to fall below 100 bpm), for 4-6 sets. In addition to having a warmup and cooldown, the 4 minutes off are important to recover as completely as possible: if you fail to cool down, you won’t be able to reach maximum effort in the next set. Attia typically has his patients do this just once a week.

Stability

Stability is to strength as endurance is to aerobic capacity. What I mean by this is that stability is explicitly not balance. Instead, it’s the subconscious ability to safely and effectively exert force. A person with good stability produces safe and effective patterns of motion without having to think about it. A stable person is versatile and seldom injures themselves.

Stability is undermined at a number of points. Over time, particularly when we spend a lot of our lives sitting, muscle groups develop relative strengths that are poorly suited to our bodies’ mechanics. We may exacerbate this process ourselves by developing asymmetric strength or compensating inappropriately for injuries. We fail to notice this process because we don’t have proper awareness of our bodies, leading us to continue to enact unhelpful patterns.

Attia takes this very seriously, and typically asks his new patients to stop any strength training they’re doing until they’ve appropriately trained stability. Unfortunately, the set of weaknesses and compensations you’ve developed will probably be pretty unique to you, and the best way to address them is likely with a trainer. Attia recommends the Postural Restoration Institute

As an example of what stability is trying to achieve, try this exercise: take a deep breath in through your nose that fills the entire cylinder of your torso, expanding your chest, stomach, sides, and back while pushing your pelvis down. When you exhale, maintain the tension in all of these areas, activating the entire cylinder of muscle around your torso in isometric compression. This cylinder of muscle is your actual core, and protects your spine. Next time you have some yard work that’s hard on your back, try doing it with this cylinder activated the entire time; you’ll find that your work is easier and less painful.

While nothing complete, Attia also has some videos relevant to stability on his website. He also recommends that you videotape your workouts (or at least a few sets) every day to make sure you’re doing what you think you are.

Strength

Though not as dramatic as VO2 max, strength is still associated with dramatically lower mortality (low muscle strength is associated with a 2x increase in mortality, so strength should reduce mortality by like 50%). Furthermore, strength is key to maintaining your independence and lifestyle. It’s extraordinarily hard to build muscle after the age of 65 or so, and by 75 you need to work out quite a lot just to avoid losing muscle. So it’s quite important to build a buffer that allows you to maintain your quality of life. Note that we’re talking about strength here, not muscle mass or hypertrophy (which is correlated, but muscle mass produced a smaller effect size, which I suspect was mediated entirely by that correlation). Moreover, this improvement seems to be more or less independent of aerobic capacity: being strong will still reduce your mortality even if you’re not aerobically healthy. A possible mechanism for this might be bone mineral density (BMD), which closely tracks muscular strength: after the age of 65, up to a third of people who fall and fracture their hips are dead within a year. Having strong bones can help make you resilient at a time in your life when you become increasingly likely to fall in the first place. You can track your BMD with a DEXA scan (the same thing that you use to measure visceral fat).

It’s important to train strength throughout your life, but building a buffer as soon as possible is wise: strength typically appears to begin declining as early as your thirties, and it becomes quite difficult to add muscle once you reach your sixties. Furthermore, our body quickly gets rid of unused muscles, especially as we age, so that more than a couple of days of rest can erase gains in the gym. While muscles are metabolically expensive (and thus good at burning extra calories), the reverse is also true: consuming excess calories can lead to muscle loss.

Attia focuses on four areas of strength:

  1. Grip strength, “which involves everything from your hands to your lats” (test: dead hang from a pullup bar, looking for 2 minutes for 40-year-old men, 90 seconds for women)
  2. Attention to concentric and eccentric loading (concentric is ability to apply force as you contract a muscle; eccentric is ability to apply it as you extend that muscle). Here the emphasis is on control, even as we lower the weight. (Test for eccentric strength: stepping off of an 18-inch block and taking a full 3 seconds to reach the ground)
  3. Pulling motions, like rows and pull-ups (test: probably pullups but Attia doesn’t say. He likes to use a rowing machine, which is also nice for VO2 max training)
  4. Hip hinging, like deadlifts, squats, step-ups, hip thrusters, split-stance Romanian deadlift, etc. (legs, glutes, lower back) (Attia doesn’t give a test for this either; usually it would be a deadlift but you should be careful on form here)

I’m not quite as convinced as Attia is by the grip strength area: he bases his enthusiasm on a number of studies correlating grip strength with lower mortality, but it seems most likely to me that this would just be a confound for overall muscular strength? In fact, Attia even admits this himself, but continues to train grip strength, apparently on the basis that having a strong grip might enable you to grab onto a branch really hard to prevent yourself from falling (with Attia’s expanded definition of grip strength, you would also be relying on your training to prevent a rotator cuff injury here - it might be better to learn how to fall).

To reiterate: you can injure yourself strength training. It’s way more important to have good movement patterns than it is to lift heavy weights. You should go into workouts with the mindset of wanting to do as few motions incorrectly as possible - even if that means cutting the workout short if you start to struggle.

Intervention 2: Nutrition

The chapter on nutrition begins inauspiciously, with Attia insisting on the phrase “nutritional biochemistry” on the grounds that longer words are less biased than shorter ones. Yet despite Attia’s own lexical biases, his thoughts on nutrition are balanced and nuanced.

One of Attia’s best qualities is starting with the most essential questions, and here the questions are: how can we expect nutrition to impact healthspan, and do we know how to produce the impacts we want? And refreshingly, Attia says: poor nutrition can hurt your lifespan, but hyper-optimized nutrition is unlikely to help it. And even if we wanted to hyper-optimize nutrition, we don’t know how.

Part of the difficulty with nutrition is that different people seem to respond to the same diet in vastly different ways. For example, some people seem to not only tolerate saturated fats well but benefit from them. But for many other people, eating saturated fat raises their levels of apoB (see: ASCVD). So it’s hard to give one-size-fits-all diet advice. However, as Attia points out, it’s very common in the nutrition world to “major in the minor and minor in the major.” If we avoid doing this, we will find it easier to develop diets that work well for us.

The three key criteria when designing your diet are:

  1. Number of calories (to ensure proper nourishment)
  2. Amount of protein (to ensure you can build muscle)
  3. Level of carbohydrates (to control metabolic health)

Attia on Diets

There are three ways to diet:

  1. Caloric restriction, which means you just eat less
  2. Dietary restriction, which means you eat less by not eating certain foods
  3. Time restriction, which means you eat less by giving yourself less time in which to eat

Attia thinks that you should do whatever works for you, but notes that fasting can result in a loss of muscle mass. Therefore, he only recommends fasting to patients for whom metabolic health is a pressing issue.

Alcohol

Most of the studies that find links between “moderate” alcohol consumption and longevity are poorly designed. No amount of alcohol has been established to be healthy, and you should restrict alcohol where it won’t impact your ability to enjoy your life.

Carbs

Different people handle carbs differently - the less metabolically healthy you are, the more harmful carbs will tend to be (creating a vicious cycle - see Metabolic Disorders). The mechanism of this harm is that carbs will tend to flood your bloodstream with glucose, which has to be dealt with as previously described. If you want to see how carbs impact your blood glucose, a Continuous Glucose Monitor (CGM) may be a good idea. You’re looking for minimal, quickly-suppressed variations in your blood glucose (basically: minimize the standard deviation). CGM technically isn’t available without a prescription, but Ageless Rx will write you a prescription for one and sell it to you for $200/month. This is a lot, but you only need it for a couple of months to discover and cement beneficial behaviors (plus maybe one a year thereafter to double-check that things are still working).

Note that there are lots of things that can impact blood glucose, which you can use to eat food you like while legitimately doing less damage to yourself. Drinking lemon juice mixed with water after a lot of glucose may spread out the load some, and eating high-fiber foods at the same time will have a similar effect. Getting your glucose after a period of fasting (like when you wake up) or exercise will also help.

Attia wants your blood glucose at or below 100 mg/dL on average, with standard deviation less than 15 mg/dL. This average is quite aggressive.

Protein

The standard recommendation I always heard for protein for building muscle was 0.5 g/lb, or 1.1 g/kg. Attia sets 1.6 g/kg as the minimum, and thinks 2.2 g/kg (1 g/lb), spread out over a full day, is ideal. As I mentioned before, this would be nine protein shakes for me. Alternately, I could eat 30 oz of meat (3 medium steaks and maybe a chicken breast). If you’re eating plant protein, Attia thinks you need even more because it’s less bioavailable (maybe 1.3x as an approximate factor).

Fat

Attia broadly recommends eating mostly monounsaturated fatty acids (55%), a bit of saturated fat (20%) and the remainder polyunsaturated fatty acids (25%), but notes that overall effect sizes here seem to be quite small. Probably this is not because it doesn’t really matter what kinds of far you eat, but mostly (by my reading) because it matters how sensitive you are to saturated fat - specifically, what it does to your apoB levels. If you seem to be able to eat a ton of saturated fat without problems (as measured by the blood test), great. Otherwise, it might be time to cut back on the steak and coconut oil.

Attia also puts all of his patients on omega-3 supplements to fix their omega 3:6 ratios, unless they already eat a ton of fatty fish.

Overview of Actionable Items

Upsettingly, unlike Sinclair, Peter Attia does not give us a place to go in his book to look at so we can see what we’re supposed to do (note: Sinclair’s section, at the very end, is technically about what he does, and to his credit he is very explicit that it may not be best for others or even himself - but it’s in his book for a reason). Is it some gambit to force us to read the whole thing and absorb the Tao of Attia? Well, I want something short to refer back to:

Random

Bloodwork

Your bloodwork will help you monitor for signs of metabolic disorders and ASCVD. For metabolic disorders, make sure:

Blood Pressure

High blood pressure can damage your endothelium and increase your ASCVD risk. Blood pressure is also cheap to monitor, even at home, and easy to modify with medication.

Body Composition (DEXA - 1x/yr)

The important factors here are amount of visceral fat and bone mineral density:

Visceral fat (these numbers do not come from the book, they’re from a random data aggregation website, meaning that they came from a bunch of very health-conscious people)

Men

Age Range In the _ Percentile 15% 35% 65% 85% Mean
19-25 Visceral Fat in lbs 0.12 0.34 0.72 1.33 0.74
26-32 Visceral Fat in lbs 0.23 0.52 1.07 1.92 1.05
33-40 Visceral Fat in lbs 0.37 0.77 1.62 2.79 1.53
41-50 Visceral Fat in lbs 0.56 1.12 2.29 3.71 2.07
51-60 Visceral Fat in lbs 0.75 1.44 2.88 4.49 2.56
60+ Visceral Fat in lbs 0.93 1.82 3.44 5.08 2.93

Women

Age Range In the _ Percentile 15% 35% 65% 85% Mean
19-25 Visceral Fat in lbs 0.02 0.16 0.46 .93 0.55
26-32 Visceral Fat in lbs 0.04 0.20 .54 1.12 .64
33-40 Visceral Fat in lbs 0.09 0.28 .71 1.46 .80
41-50 Visceral Fat in lbs 0.16 .40 1.03 1.96 1.05
51-60 Visceral Fat in lbs 0.25 .59 1.39 2.44 1.32
60+ Visceral Fat in lbs 0.47 .92 1.82 2.85 1.63

BMD (bone mineral density) You’ll receive a T-score, which compares your BMD to that of a healthy young adult. A T-score of 0 is equivalent, less than -1 is bad. More than 0 is extra credit.

Waist:height ratio This is a reasonable proxy for body composition, and you ideally want it below 1:2

Exercise Metrics