The 4-Hour Body: The Glucose Switch and the Last Mile of Fat Loss

Tim Ferriss is standing in an airport security line with a medical sensor implanted in his abdomen. His hands are sweating. He almost wore a 50-pound weighted vest through TSA, but a friend talked him out of it by pointing out it looked like a suicide bomber jacket. So the vest stayed home. But the implant made it through just fine.

Welcome to Chapter 12.

Chapter 12: The Glucose Switch

Tim met a medical device designer at a dinner party in San Francisco. The guy mentioned something called DexCom - a continuous glucose monitor. Originally built for diabetics. A small sensor goes under your skin, samples your blood glucose every five seconds, and sends data to a little receiver that shows your numbers on a graph.

A race car driver named Charlie Kimball was using one strapped to his steering wheel. He is a type 1 diabetic who couldn’t prick his fingers while doing 150 mph around corners. The DexCom let him race again.

Tim’s brain immediately went to a different place. What if a non-diabetic could use this thing to figure out which foods make you fat? Not in theory. Not from a chart on the internet. Your actual body, your actual blood, in real time.

So he got one implanted and started logging everything.

What the Data Showed

Here is the thing about blood sugar that most people get wrong. It is personal. The glycemic index charts you find online are averages tested in labs. Your body is not an average. Someone from a bread-eating European family processes starch differently than someone from a pastoral culture that mostly ate meat. They have different amounts of amylase enzyme. Same food, different response.

Tim spent weeks eating, measuring, writing down every meal in a Moleskine notebook, and comparing it to his glucose graph. Here is what he found.

Food hits your blood way later than you think. Most foods peaked one and a half to two and a half hours after eating. Even yogurt. Orange juice was the fastest at 40 minutes. This means if you eat a snack “for energy” 20 minutes before the gym, that energy probably arrives an hour after you finish working out. You need to eat earlier. Same with post-workout protein shakes - Tim found he needed to drink his shake before the workout, not after.

Fat blunts glucose spikes better than lean protein. Eating fat early in the meal made the biggest difference. Tim started eating four Brazil nuts and a tablespoon of almond butter first thing every morning. Fat before carbs, not the other way around.

Fructose is a trap. Orange juice kept Tim’s glucose line flat and low, which looks great on a graph. But his fat-loss stopped. Low blood sugar does not always mean more fat burned. The fructose was doing something else entirely. As Warren Buffett says - measure what matters. If the goal is fat loss, the scale and body fat percentage are what count, not a pretty glucose number.

Vinegar did nothing. Lemon juice worked. This was a surprise. Vinegar lowering blood sugar is one of those things “everybody knows.” Tim tried white vinegar, balsamic vinegar, even drinking three tablespoons before meals. Nothing happened. But three tablespoons of fresh-squeezed lemon juice before eating lowered his glucose peaks by about 10%. No one could find a published study proving lemon juice does this, but it worked for him consistently.

Cinnamon is legit. Published research shows cinnamon can reduce the glycemic response of a meal by up to 29%. Tim tested three types: Ceylon, Cassia, and Saigon. Saigon worked best, Cassia was close behind, Ceylon was a distant third. Cassia is what you find at most coffee shops when you ask for cinnamon. Important: do not go crazy with it. Four grams per day max - about one and a half teaspoons. Cinnamon has a blood-thinning compound called coumarin, and too much is bad.

Slow down your eating. Even eating just protein and vegetables, Tim could spike his glucose to 150 mg/dL by eating fast. He had to train himself to eat in thirds with five-minute pauses. Matt Mullenweg, the WordPress creator, lost 18 pounds just by chewing each bite 20 times. Argentine women eat garbage calories but stay thin because they eat slowly and in small portions. Then they move to the US, eat faster and more, and gain 10-20 pounds.

The 100 Rule

Tim’s practical takeaway: keep blood sugar bumps above 100 mg/dL to no more than twice per day. Below 90 was even better, but hard to maintain without going full ketogenic. The slow-carb diet naturally keeps you under this threshold if you eat decent fat with each meal, take 30+ minutes per meal, and use cinnamon or lemon juice.

You do not need an implant to follow these rules. They work regardless.

Chapter 13: The Last Mile

Now for the hard part. You already lost the easy weight. You are maybe 10-12% body fat. You look good. But you want to look great. Those last 5-10 pounds are stubborn.

Tim interviewed John Romano, the editor in chief of Muscular Development magazine, who had been watching bodybuilders experiment on themselves for over twenty years. Romano’s first move was funny. Tim asked about “natural” bodybuilders. Romano laughed: “The biggest mistake natural bodybuilders make is thinking they’re natural. Eating 20 chicken breasts a day isn’t natural. The best I’ll give them is ‘over-the-counter.’”

The Last Mile Diet

Romano and his business partner Dave “Jumbo” Palumbo developed a simple diet for cutting the last stubborn fat. It is strict, but it is clear. For a 200-pound male at 10-12% body fat, you eat one of these meals every three hours while awake:

• 50g whey protein isolate + half cup of nuts or 2 tbsp peanut butter
• 8oz cooked white fish + half cup nuts or 2 tbsp peanut butter
• 8oz chicken or turkey + half cup nuts or 2 tbsp peanut butter
• 8oz fattier protein (red meat, dark poultry) + 1 tbsp olive or macadamia oil
• 5 whole eggs

You must eat within one hour of waking and one hour of going to bed. No skipping meals. The clock tells you when to eat, not your stomach.

Unlimited green vegetables at every meal: spinach, asparagus, Brussels sprouts, kale, broccoli. No corn, beans, tomatoes, or carrots. One cheat meal every seven to ten days.

Adjust protein by 1 ounce per 10 pounds of lean bodyweight. Never go below 4 ounces per meal even if you are small.

Simple. Repetitive. Effective. Gets you to 8% body fat or less.

Below 8%: The Drug Discussion

Romano also outlined what bodybuilders do to get below 4% for competitions. That section is a laundry list of anabolic steroids, growth hormone, and other drugs with a schedule that reads like a NASA launch checklist. I am not going to reproduce the specifics here because if you need that information, you are way past blog posts.

What is interesting is the book’s broader point about steroids. Tim points out that birth control pills are steroids. Cortisone shots are steroids. Without steroids your body would die. The scary side effects people associate with them - swelling, breathing problems, bloody vomit - Tim reveals those are actually the listed side effects of aspirin. He is not encouraging recreational use. He is saying the hysteria is disproportionate to the science.

The dose makes the poison. A glass of wine before bed versus drinking bottles until you are in the ICU. Same substance, very different outcomes.

My Take

Chapter 12 is probably one of the most practically useful chapters in the entire book. The glucose monitor experiment is cool, but the real value is the takeaways you can use without any gadgets. Eat fat first. Use lemon juice. Add cinnamon. Slow down. Stay under 100 mg/dL twice a day max. These are tiny changes with real effects.

Chapter 13 is more niche. If you are already lean and want to get leaner, the every-three-hours protein protocol is a good tool. The steroid discussion is honest and refreshing, even if you never plan to touch any of it.

The combination of these two chapters shows Tim’s full range. One chapter is about a guy pulling a sensor out of his stomach in an airport restaurant. The next is about eating Tupperware meals on a timer. Both serve the same goal: stop guessing, start measuring, and do what actually works.

Previous: The Four Horsemen of Fat-Loss and the Ice Age

Next: Building the Perfect Posterior and Six-Minute Abs

This is part of my 4-Hour Body retelling series. New posts every Saturday.