Why we eat (too much)

If you've dieted, regained, and blamed yourself, this book hands you a different explanation—and a way out. It's for anyone caught in the cycle of restriction and rebound, or confused by decades of conflicting nutrition advice. Jenkinson, a practicing surgeon, writes with clinical authority but zero judgment.

1. 1Part 1: The Science of Weight Gain

   Your body fights your diet like a thermostat fights an open window

   Jenkinson says your body does the same with weight. When patients lose weight, their resting metabolic rate drops disproportionately—someone who loses 10% of body weight may burn 20-25% fewer calories than a person of the same weight who was never obese. The body defends its set point, adjusting metabolism and hunger like a thermostat regulating temperature. Dieters aren't weak; they're fighting their own biology.

   The idea

   Weight isn't a simple ledger of calories in versus calories out. Your body actively defends a set weight range, and when you cut calories, it responds by slowing your metabolism and amplifying hunger until the weight returns. This explains why nearly every diet works briefly and then fails. The set point itself is the real target—not the number on the scale this month.

   Try this: Stop judging a diet by the first two weeks. Track how hungry you feel at week six—if you're ravenous, your set point is fighting back, and the approach won't last.

2. 2Part 1: The Science of Weight Gain

   Leptin: the hormone that tells your brain you're full—until it stops working

   In a healthy body, that message lands. Fat stores are ample, leptin is high, appetite backs off. Now imagine the brain slamming the door on the messenger. That's leptin resistance. In obesity, fat cells keep producing the hormone, keep sending the signal—and the brain stops hearing it. Convinced it's starving, the brain cranks up hunger even as fat reserves pile up.

   The idea

   Obesity isn't a character flaw—it's a signaling failure. Fat cells are screaming 'we're full' but the brain can't hear them anymore. This reframes overeating as a hormonal communication breakdown, not a moral one. The question shifts from 'why can't you stop eating?' to 'why can't your brain hear the stop signal?'

   Try this: Notice when you feel hungry shortly after a large meal. That disconnect—full stomach, hungry brain—is worth flagging to yourself as a possible leptin signal problem, not a lack of discipline.

3. 3Part 1: The Science of Weight Gain

   Insulin is the lock on your fat cells

   The difference isn't discipline—it's insulin. As the body's primary fat-storage hormone, insulin decides whether energy gets burned or locked away in adipose tissue. Keep it chronically high and the fat stays locked. Stress compounds this: cortisol raises blood sugar and insulin, and chronic stress can shift the weight set point upward while pushing fat toward the abdomen. Same meal, different bodies, different outcomes.

   The idea

   You can't burn fat if insulin is always elevated—it's the hormone that locks fat away in storage. Chronically high insulin, driven by frequent eating, refined carbohydrates, or chronic stress, keeps the door shut. This is why some people eat less and still don't lose weight: their insulin won't let them access their own fat.

   Try this: Notice how many hours you go between eating today. If you're grazing from morning to night, your insulin never gets a chance to drop.

4. 4Part 1: The Science of Weight Gain

   The omega-6 overload hiding in your kitchen

   The ratio of omega-6 to omega-3 fatty acids in your cell membranes influences how sensitive your cells are to insulin. Modern vegetable oils push this ratio skyward. A high omega-6 ratio from these oils promotes insulin resistance and inflammation.

   The idea

   The type of fat you eat changes your cell membranes, and those membranes determine how well insulin works. A diet heavy in omega-6 vegetable oils creates insulin resistance at the cellular level, independent of how many calories you consume. This is a structural problem, not a behavioral one.

   Try this: Check the ingredient list on your cooking oil. If it says soybean, corn, or canola, consider swapping it for olive oil or butter this week.

5. 5Part 2: The Environmental Triggers

   The Minnesota Starvation Experiment: what happens when you eat 1,570 calories a day

   36 conscientious objectors volunteered for the Minnesota Starvation Experiment. They were put on a 1,570-calorie semi-starvation diet for 24 weeks. They lost 25% of their body weight—but they became obsessed with food, thinking about it constantly. When refeeding began, many binged uncontrollably and regained weight rapidly.

   The idea

   This experiment shows what happens when you force the body below its set point: obsession, bingeing, and rapid regain. It's not weakness—it's predictable biology. Every crash diet recreates these conditions in miniature. The subjects weren't gluttons; they were starving men whose bodies demanded recovery.

   Try this: If you've ever 'fallen off' a strict diet and binged, recognize that as a biological response to restriction—not a personal failure. Try a less aggressive deficit this week.

6. 6Part 2: The Environmental Triggers

   Fructose: the sugar that bypasses your fullness signal

   Fructose, unlike glucose, is metabolized almost entirely by the liver. There, it can be converted to fat and promote insulin resistance. Crucially, fructose does not stimulate insulin or leptin—the hormones that control appetite. It bypasses your fullness signals entirely. Endocrinologist Dr. Robert Lustig calls it 'alcohol without the buzz.'

   The idea

   Fructose is uniquely problematic because it skips the appetite-control system. You can drink 500 calories of orange juice and feel no less hungry. Meanwhile, your liver converts the excess to fat and develops insulin resistance. This is why liquid sugar—soda, juice, sweetened coffee drinks—is particularly damaging.

   Try this: Replace one liquid sugar source today—juice, soda, or a sweetened latte—with water, sparkling water, or unsweetened tea.

7. 7Part 2: The Environmental Triggers

   Seed oils went from 2% to 7% of our calories

   Vegetable oils like soybean and corn oil, high in omega-6 linoleic acid, have increased in the food supply from about 2% of calories in 1900 to over 7% by 2000. Their consumption correlates with rising obesity rates. Meanwhile, trans fats—created by partially hydrogenating vegetable oils—were introduced in the early 20th century and were finally banned in the US in 2018 after being linked to heart disease and inflammation.

   The idea

   The oils in processed food aren't neutral. They've gone from a tiny fraction of our diet to a significant portion in just 100 years, and obesity rates have tracked alongside. Trans fats took a century to ban. The current omega-6 overload may be a slower version of the same story.

   Try this: Count how many packaged foods in your kitchen list vegetable oil, soybean oil, or sunflower oil in the first three ingredients. Aim to replace one this week.

8. 8Part 2: The Environmental Triggers

   The Pima Indians: same genes, different food, 10x the diabetes

   A study compared Pima Indians in Arizona with Pima Indians in Mexico—same genetic population, different food environments. Arizona Pimas, eating a Western diet, had an average BMI of 36 and a 65% diabetes rate. Mexican Pimas, eating traditional foods, had an average BMI of 25 and a 6% diabetes rate. Same genes. Ten times the diabetes. The difference was what was on the plate.

   The idea

   When genetics are held constant and only the food environment changes, obesity and diabetes follow the food—not the genes. This is one of the cleanest natural experiments in nutrition.

   Try this: Look at your own food environment—what's within arm's reach right now? Move one processed snack out of sight and put a whole food in its place.

9. 9Part 2: The Environmental Triggers

   Sarah ate 'healthy' and couldn't lose an ounce

   Sarah, a 42-year-old patient, ate a low-fat, high-carbohydrate diet and exercised regularly. She could not lose weight. Her fasting insulin was 15 mIU/L—the normal range is 2-6. She had severe insulin resistance. Despite doing everything the standard advice told her, her hormones were working against her.

   The idea

   Sarah followed the rules and still couldn't lose weight because her insulin was chronically elevated. The standard advice—eat less fat, eat more carbs, exercise more—doesn't address insulin resistance. For someone in Sarah's state, the low-fat approach actively worsens the hormonal problem.

   Try this: If you've been eating low-fat and high-carb without results, consider getting your fasting insulin tested. Normal is 2-6 mIU/L.

10. 10Part 2: The Environmental Triggers

    Tom drank 2 liters of orange juice a day

    Tom, a 55-year-old patient, drank 2 liters of orange juice daily because he thought it was healthy. He had a fatty liver and fasting triglycerides of 350 mg/dL. After cutting out liquid fructose, his triglycerides normalized.

    The idea

    Fruit juice is marketed as healthy but delivers a concentrated fructose load directly to the liver. Tom's fatty liver and elevated triglycerides reversed when he stopped. The dose matters—2 liters is extreme, but even moderate daily juice contributes to the same pathway.

    Try this: If you drink fruit juice daily, try replacing it with whole fruit this week. The fiber changes everything.

11. 11Part 2: The Environmental Triggers

    The Women's Health Initiative: 48,835 women, 7.5 years, zero weight loss

    The Women's Health Initiative Dietary Modification Trial followed 48,835 postmenopausal women for 7.5 years. They reduced fat intake to 29% of calories. They did not lose weight compared to the control group. There was no reduction in heart disease. One of the largest and longest dietary trials ever conducted produced no benefit from the low-fat approach.

    The idea

    The low-fat hypothesis was tested at massive scale and failed. Nearly 50,000 women, nearly 8 years, and no weight loss, no heart disease reduction.

    Try this: Don't fear fat. This week, include a source of healthy fat—olive oil, avocado, or nuts—with each meal.

12. 12Part 2: The Environmental Triggers

    The average American eats 77 pounds of added sugar a year

    The average American consumes about 77 pounds of added sugar per year, much of it hidden in processed foods. In the early 1800s, added sugar consumption was negligible by comparison. Jenkinson states: 'The obesity epidemic is not a failure of willpower; it is a failure of our food environment.'

    The idea

    77 pounds a year is over a pound of added sugar per week, much of it invisible in processed foods.

    Try this: Read the label on three packaged foods you eat regularly. Look for sugar under its many names. Pick the one with the most and find a lower-sugar alternative.

13. 13Part 3: The Solution

    Skip the snacks, shrink the eating window

    Jenkinson advises against snacking. Constant eating keeps insulin chronically elevated. He suggests 2-3 meals per day without snacks to allow insulin to fall between meals. He also recommends intermittent fasting or time-restricted eating, such as a 16:8 pattern—fasting for 16 hours, eating within an 8-hour window—to lower insulin levels and allow the body to access fat stores.

    The idea

    Fewer eating occasions and a compressed eating window give insulin a chance to fall, unlocking fat stores for energy.

    Try this: Try a 16:8 pattern this week: stop eating at 8pm, don't eat until noon the next day. Water, black coffee, and plain tea are fine during the fast.

14. 14Part 3: The Solution

    Eat fat that doesn't fight your cells

    Jenkinson recommends reducing omega-6 vegetable oils by avoiding processed foods and using butter, olive oil, or coconut oil instead, to lower the omega-6 to omega-3 ratio toward the ideal of 4:1 or lower. He also advises limiting fructose to no more than 25 grams per day—roughly the amount in one piece of whole fruit—and avoiding high-fructose corn syrup and fruit juices.

    The idea

    Two specific targets: lower your omega-6 intake by changing your oils, and cap fructose at 25 grams daily. The omega-6 to omega-3 ratio should be 4:1 or lower.

    Try this: This week, replace all vegetable oil in your kitchen with olive oil or butter, and check fruit juice and HFCS at the door.

15. 15Part 3: The Solution

    Protein and sleep: the two levers nobody pulls

    Jenkinson recommends eating adequate protein—about 1.2 to 1.6 grams per kilogram of body weight per day—to promote satiety and preserve muscle mass during weight loss. He also emphasizes sleep quality: one night of 4 hours of sleep reduces insulin sensitivity by 20-30% in healthy individuals, and chronic sleep deprivation is linked to weight gain.

    The idea

    Protein keeps you full and protects muscle while losing weight. Sleep, often ignored, directly controls insulin sensitivity—a single short night reduces it by 20-30%. These are foundational inputs that most diet plans skip entirely.

    Try this: Calculate your protein target: multiply your weight in kg by 1.2. Aim for that many grams daily, and get 7+ hours of sleep tonight.

16. 16Part 3: The Solution

    Your body is not a calculator

    Jenkinson writes: 'Your body is not a simple calorie calculator; it is a complex hormonal system that adapts to the signals you send it.' He also writes: 'The most powerful tool for weight loss is not a diet, but an understanding of how your body's hormonal systems work.' The goal isn't to find the right diet—it's to understand the signals.

    The idea

    Stop looking for the perfect diet. Start understanding the signals—insulin, leptin, omega-6 ratio, sleep, stress—that shape your weight set point.

    Try this: Pick one hormonal signal from this book—insulin, sleep, or omega-6—and focus on improving just that one this week.

Anyone who has dieted, regained, and wondered what's wrong with them. Also essential for anyone eating a modern processed diet who wants to understand why their body is fighting back.

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