I wore a continuous glucose monitor on the back of my arm, more or less continuously, for nearly three years.
Thirty-three months. 262,000 glucose readings. Every meal, every workout, every stressful Zoom call, every late night, every coffee — all of it tracked in real time by a sensor the size of a quarter reading my blood chemistry every few minutes. I ranked 187 foods by their glucose spike impact on my own metabolism. I found that summer on Cape Cod did measurably better things to my metabolic health than winter in San Francisco (96 mg/dL average vs. 101). I learned which supplements spiked my glucose, which ones didn’t, and which breakfast sent my blood sugar into a slow grind that didn’t resolve until noon.
I am telling you this not to brag about my commitment to data, but because the single most important thing my CGM taught me has nothing to do with data.
It is four words.
Eat real f*cking food.
That’s the Nutrition pillar of the Slowfit Method®. Four words. Everything else — the macros, the timing, the supplements, the fasting windows, the protein targets — is built on top of that foundation. If you get the foundation wrong, none of the optimization matters.
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The book you need to read right now
Dr. Chris van Tulleken is a British physician, BBC journalist, and infectious disease researcher at University College London. For his book Ultra-Processed People: Why We Can’t Stop Eating Food That Isn’t Food, he spent a month eating 80 percent ultra-processed food while scientists monitored everything that happened to his body and brain.
He gained weight. His appetite regulation broke down. His gut microbiome degraded. His mood deteriorated. His desire for the UPF foods increased even as they made him feel worse — a textbook addiction response.
Then he stopped. And everything reversed.
Van Tulleken’s argument is not that ultra-processed food is unhealthy in the way that, say, too much salt is unhealthy. His argument is that UPF is not food. It is an industrially manufactured substance, engineered from cheap commodity inputs, designed in laboratories to override the satiety signals that evolution built into us over millions of years. The goal is not to nourish you. The goal is to make you eat more of it.
What is UPF? The working definition — the NOVA classification system — is not about calories or fat or sugar per se. It is about degree of industrial processing. If it contains ingredients you would not find in a home kitchen, if it has been assembled from components extracted from other foods, if its texture and flavor were designed to maximize palatability and minimize fullness — it is ultra-processed. This covers roughly 60 percent of the American diet. It covers most of what is in the middle aisles of your grocery store. It covers a lot of what you think of as “healthy” options.
Ultra-Processed People is the most important food book I have read since Robert Lustig’s Metabolical. It belongs at the top of your list. And the news is not all grim: Van Tulleken is not asking you to be perfect. He is asking you to understand what you are eating. Because once you understand it, the choices get easier.
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The Lustig framework: it’s not the calories
Dr. Robert Lustig is a neuroendocrinologist at UCSF who has spent decades studying the metabolic effects of sugar and ultra-processed food. His book Metabolical makes the case that the chronic disease epidemic — obesity, type 2 diabetes, heart disease, cancer, Alzheimer’s — is not the result of personal failure or lack of willpower. It is the predictable result of an industrialized food supply that has been systematically engineered to maximize profit at the expense of metabolic health.
The core Lustig insight, summarized: sugar, and specifically fructose, drives insulin resistance and liver dysfunction in ways that do not show up in simple calorie counts. A calorie of fructose is not a calorie of glucose is not a calorie of fat. The “a calorie is a calorie” framework that dominated dietary science for fifty years was wrong, and it was convenient for the food industry for it to be wrong.
What to do about it: reduce added sugar, read ingredient labels, and default to foods that were not manufactured in a facility. The rule I use with every athlete I coach: if your great-grandparents would recognize it as food, it probably is.
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You lose weight in the kitchen, not the gym
Herman Pontzer is a Duke evolutionary anthropologist who has spent his career studying human metabolism across cultures and activity levels. His research produced a finding that shocked the fitness world: the Hadza hunter-gatherers of Tanzania, who walk eight to ten miles a day hunting and foraging, burn roughly the same number of total calories as sedentary Western office workers.
The body adapts. Exercise is not primarily a weight management tool. It is a metabolic health tool, a cardiovascular tool, a bone density tool, a mental health tool, a longevity tool — but it is not the way to outrun a bad diet. You cannot out-train poor nutrition. The research is definitive on this.
The implication is not that exercise doesn’t matter. It matters enormously, for all the reasons above. The implication is that if your goal includes body composition, food is the primary lever. Exercise is the multiplier.
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The protein argument you need to hear
Dr. Gabrielle Lyon’s Forever Strong makes the case that the medical establishment has been asking the wrong question. The focus has been on fighting fat. The real lever is building muscle.
Muscle is not just the thing that makes you look good at the beach. It is the body’s largest endocrine organ, the primary site of glucose disposal, the tissue most responsible for metabolic health and aging trajectory. Sarcopenia — the loss of muscle mass with age — is a more powerful predictor of mortality than obesity. And the solution is resistance training plus adequate protein.
Lyon’s prescription: one gram of protein per pound of lean body mass per day, minimum. This is higher than conventional recommendations and significantly higher than most people are actually consuming. She also makes the case for protein timing — prioritizing protein at breakfast rather than backloading it at dinner, and hitting a post-training protein window within 45 minutes of finishing a session.
The Momentous protein I use with athletes (code: FOGHORN) is NSF Certified for Sport and among the most rigorously tested on the market. If you are not hitting your protein targets from whole food sources, a quality protein supplement is not a crutch — it is a tool.
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What 33 months of CGM data actually showed me
After 33 months of continuous glucose monitoring, here is what my own data showed me.
The foods with the highest and most consistent glucose spikes were exactly what you would expect: refined carbohydrates, sugary drinks, white rice, most bread, processed snacks. The foods with the lowest impact: vegetables, proteins, healthy fats, legumes.
What surprised me: how much stress spiked my glucose independent of food. A difficult conversation. A contentious Zoom call. A piece of bad news. These produced glucose responses nearly indistinguishable from a modest meal — without a single bite of food. The connection between the stress response and metabolic health is real and measurable.
What the data confirmed: 97.6 percent of my readings were in the healthy range (70-140 mg/dL). My mean glucose across the entire dataset was 99.7 mg/dL. I attribute this primarily to three things: real food as the foundation, consistent exercise, and — after taking a hard look at my relationship with it — no alcohol.
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The alcohol honest conversation
Alcohol is part of the Nutrition pillar in the Slowfit Method®, and I am not going to soft-pedal it.
I stopped drinking nearly four years ago. Not because I had a problem by conventional definitions. Because the data was unambiguous — alcohol suppressed my REM sleep, elevated my resting heart rate, degraded my recovery scores, and spiked my cortisol in ways that took 48 hours to fully resolve. A drink or two on a Friday night was affecting my Tuesday training.
The U.S. Surgeon General issued an advisory in January 2025 declaring alcohol the third leading preventable cause of cancer in the United States, calling for updated warning labels. This came after decades of research suggesting a “safe” level of consumption. The current scientific consensus is that there is no safe level when it comes to cancer risk specifically.
I am not here to tell you how to live your life. I am here to be honest with you about what the research shows, and what I have experienced firsthand. If you are working on performance, recovery, sleep, or body composition, alcohol is working against all of them. That is just the truth.
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Practical takeaways
Start with real food. If it grew somewhere or had a mother, it is probably food. If it was designed by a bunch of scientists and assembled in a factory from industrial inputs, it is probably not. This is not a complete nutrition system. It is a foundation. Build on it from there.
Read the ingredient list. Not the nutrition facts label — the ingredient list. If it contains more than five ingredients, or ingredients you cannot pronounce, think twice. Van Tulleken’s rule: if your great-great-grandmother would not recognize it as food, it probably is not.
Hit your protein target. Bodyweight in grams, minimum. Prioritize it at breakfast. Do not skip the post-training window.
Consider a CGM. Even a month of continuous glucose monitoring will tell you more about how your body responds to specific foods than any diet book. Levels Health is the platform I used for nearly three years. The data is genuinely eye-opening and I’d recommend it to any athlete serious about metabolic health.
Reduce added sugar. Specifically fructose in processed form — not fruit, not whole food sources. The ingredient list will tell you where it is hiding. High-fructose corn syrup, cane sugar, dextrose, maltose — there are 60-plus names for added sugar on labels.
Get honest about alcohol. You do not have to quit. But look at your Whoop data on nights you drink versus nights you do not and decide for yourself what the data is telling you. Or maybe read the alcohol post I shared awhile back; here ‘tis.
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The Slowfit Method® app puts Coach Keir AI in your pocket — trained on all ten pillars including this one. Ask it anything about your nutrition, what to eat before training, how to manage glucose, what ultra-processed food is doing to your body, or how to hit your protein targets. One hundred people have already downloaded this app, and I’ve got nine 5-star reviews on the App Store. Check it out!
I’ve added an easy way to book a free 30-minute introductory call with me to learn more about the Slowfit Method® and/or my AI Coach app, to discuss your training goals, or to explore what a private coaching relationship might look like. No pressure, no pitch — just a conversation.
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Stick around.
Best,
Keir
Keir J. Beadling is a human performance coach, founder of Foghorn Fitness, and creator of the Slowfit Method®. He coaches athletes and everyday humans in San Francisco and worldwide. More information is available at foghornfitness.com.
The Lemonade Chronicles 