The 4-Hour Body: How to Measure Bodyfat and Use Photos for Motivation
Your scale is lying to you. Not on purpose. It just doesn’t know any better.
That’s the message from chapters 5 and 6 of The 4-Hour Body. And honestly, once you read the data, you’ll never look at your bathroom scale the same way.
The Scale Problem
Tim tells the story of Subject X - a 65-year-old man who lost 41 pounds in the first three months. Great, right? But then in the next four months, he only lost 8 more pounds. He was getting depressed about it.
Here’s the thing. During those “slow” months, the guy nearly tripled his strength on every exercise. He went from pressing 15 pounds to 75 on shoulder press. From 50 to 135 on pulldowns. That’s not someone stuck in a plateau. That’s someone building muscle while losing fat at the same time.
If you estimated even 10 pounds of new muscle (which is conservative given those strength numbers), his actual fat loss was closer to 18 pounds, not the 8 his scale showed.
That man was Tim’s father. He went from 245 pounds to 173. His doctor told him he was “younger now than a year ago.” But he almost quit during his best months because of a number on a cheap device.
So How Do You Actually Measure Bodyfat?
Tim did what Tim does. He measured his bodyfat using every method he could find, all within 24 hours. The results ranged from 7% to 16.5%. Same body, same day, wildly different numbers.
Here’s what he tested:
- 3-point calipers - 7%
- Accu-measure - 7.1-9.4%
- BodyMetrix ultrasound - 9.5%
- DEXA scan - 11.3%
- BodPod - 13.3%
- Omron hand-held bio-impedance - 14.7-15.4%
- 4-site calipers - 15.5-16.5%
None of them are perfectly “accurate.” And that’s Tim’s point. Accuracy doesn’t matter as much as consistency. Pick one method and stick with it. What matters is the trend over time, not the absolute number.
The Top 3 Methods
After testing everything, Tim settled on three winners based on reliability and convenience.
1. DEXA ($50-100 per session). This is an X-ray based scan. Originally designed for bone density testing, it also shows you muscle mass distribution by body region. Tim found it useful for spotting left-right muscle imbalances. His left trunk had a full kilogram more than his right. Stuff like that helps prevent injuries. You can find DEXA at medical facilities - Google your city plus “DEXA body fat.”
2. BodPod ($25-50). You sit in a sealed capsule. Air pressure changes measure your body composition. It’s the same tech the NFL uses at their combine to evaluate 330 top college football players. It works for anyone up to 500+ pounds, which makes it better than calipers for heavier people.
3. Ultrasound/BodyMetrix. A hand-held device that shows exact fat thickness in millimeters wherever you place it. Teams like the New York Yankees and AC Milan use it. Tim ended up using this one the most because it was quick and easy. The professional unit costs about $2,000, though a cheaper personal version was in development.
What If You Can’t Find the Fancy Stuff?
Fair enough. Not everyone has a DEXA machine nearby. Tim gives some rules for the budget options:
Bio-impedance devices (scales, hand-held): Your hydration level changes the reading a lot. Tim made his bodyfat jump 1% in five minutes just by drinking two liters of water. His fix: drink 1.5 liters of cold water right when you wake up, wait 30 minutes, pee, then test. Same routine every time.
Calipers: Different math formulas give different results on the same calipers. Ask for a 3-point or 7-point Jackson-Pollock algorithm. Always use the same person to measure you. And always include a leg measurement - leg fat is tricky and throws off the numbers if you skip it.
And the most important rule: never compare results from different tools. If you start with BodPod, stick with BodPod. Mixing methods gives you garbage data.
Eyeballing It
The book includes a visual guide for estimating bodyfat by how you look. Quick version for men:
- 20% - No muscle definition visible
- 15% - Some separation in shoulders and upper arms. No visible abs
- 12% - More separation in chest and back. Outline of abs starting to show
- 10% - Six-pack visible when flexed
- 7-9% - Abs visible all the time. Veins showing in arms. Face gets angular
- 5-7% - Bodybuilder competition level. Striations in muscles
Tim’s recommended goals: men who are obese should aim for 20%, men with a bit extra should aim for 12%. For women: 25% and 18% respectively.
Your Physical GPS - The Starting Steps
Tim begs you not to skip this part. His dad still kicks himself for not getting baseline bodyfat numbers. Here’s the minimum:
- Measure circumference with a tape measure at four spots: both upper arms (mid-bicep), waist (at navel), hips (widest point), both legs (mid-thigh). Add them up for your Total Inches number.
- Estimate your bodyfat using the visual guide above.
- Schedule a proper test - DEXA if you can find it, BodPod as second choice, ultrasound third.
Track these over time and you’ll always know if you’re heading the right direction, even when the scale says nothing is happening.
Chapter 6: From Photos to Fear
Now here’s where things get interesting. Chapter 6 is about making yourself follow through. Because knowing what to do and actually doing it are very different things.
Tim opens with the story of Trevor, who went from 240 pounds to under 200. How? He made a bet with a coworker. One dollar per missed gym session. That’s it. One dollar.
His first gym visit was four minutes on a treadmill. Four minutes. Not long after that, he ran a mile for the first time since fourth grade. Eventually he ran two half-marathons.
It wasn’t about the dollar. It was about the psychology of not wanting to lose.
Four Principles of Failure-Proofing
Tim breaks down four ways to make it almost impossible to quit:
1. Make it conscious. Researchers at University of Wisconsin had people photograph every meal before eating it. No diet rules, just photos. People naturally made better choices because who wants to take a photo of a jumbo bag of M&Ms? Studies showed photo journals beat written food diaries. And food diaries already triple weight loss compared to no tracking at all.
Also: take “before” photos. Winners of the Body-for-Life Challenge, the biggest physique transformation contest in publishing history, all credited one thing - their “before” photos taped to the fridge. Get an honest picture of where you are. It will look worse than you expect. That’s the point.
2. Make it a game. Tim tells the story of Jack Stack, who bought a near-bankrupt engine company with $100,000 against a $9 million loan. The bank officer who approved it got fired. But Stack turned it around by putting all the numbers on grease boards around the plant. Daily goals, daily tracking, daily recognition. That $100K became $23 million in 10 years.
The science backs this up. Nike+ found that once runners logged five sessions, they were massively more likely to keep going forever. Five is the magic number. Five workouts, five meals on plan, five of whatever new habit you’re building.
3. Make it competitive. Research from NYU showed people work harder to avoid losing $100 than to earn $100. Fear of loss beats desire for gain. Data from DailyBurn (500,000+ users) confirmed it - people in competitive challenges lost 5.9 more pounds than solo users. And those with three or more peers in their group lost 5.8 more pounds on top of that.
Tim’s friend Ramit Sethi put this to work. Ramit bet friends about $8,000 total that he could gain 15 pounds of muscle in three months. He set up a public wiki page where everyone could see his progress. Then he talked massive trash. He gained over 15 pounds, kept his bodyfat low, and maintained that weight three years later. His advice: “Use psychology to help. Don’t just ’try harder.'”
4. Make it small and temporary. This is maybe the most practical piece. Author Michael Levin writes two pages per day. Dr. B.J. Fogg from Stanford wrote one sentence per day for his dissertation and finished in record time. IBM dominated sales for decades by giving reps the lowest quotas in the industry - just get them to pick up the phone.
Don’t commit to six months of meal prep. Commit to two weeks. Don’t start with an hour of walking. Start with five minutes. Five sessions of anything, made as painless as possible. Momentum handles the rest.
The Phil Libin Experiment
The chapter ends with a great story. Phil Libin, at 258 pounds, decided to lose weight by doing… nothing. Well, almost nothing.
He drew a target line in Excel from 258 to 230 over two years. Every day’s target was only about 0.1% lower than the day before. He weighed himself naked every morning, same time, before eating. That’s it. No diet changes. No exercise. He made a deliberate effort NOT to change anything.
He lost 28 pounds in six months. Just from awareness.
The few times his weight dipped below his minimum target? He ate doughnuts to get back in the safe zone. That’s commitment to the experiment.
His theory: awareness affected thousands of tiny unconscious decisions throughout each day. He just couldn’t tell you which ones.
Bottom Line
Your scale tells you one number. That number is incomplete. Measure bodyfat, measure circumference, take photos. Then use bets, competition, and small commitments to actually stick with it.
Track or you will fail. Those are Tim’s words, not mine. But I think he’s right.
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This is part of my 4-Hour Body retelling series. New posts every Saturday.