Plans for Your Body · Food & fasting
The intermittent fasting plan
Stop eating all day. Your insulin needs the night off.
The goal: Intermittent fasting works by giving insulin long, regular breaks so your body can draw on stored fat. Check your medications first, shrink your eating window over two weeks, add one longer fast a week, eat enough protein to keep your muscle, and retest your numbers at 3–6 months.
The average person eats from the moment they wake to the moment they go to bed, then wonders why insulin never comes down. Intermittent fasting isn’t a diet; it’s a schedule. It changes when you eat, which changes how much time your body spends storing fat versus burning it. Done badly, it’s skipped breakfast and a 10 pm binge. This plan does it properly.
- CheckMedications · pregnancy · eating-disorder history · your doctor’s OK
- MeasureWeight · waist · fasting insulin and glucose · HbA1c · lipids
- Fast12 → 14 → 16 hours over two weeks · then one 24–36-hour fast a week
- ProtectProtein at every meal · lift 2–3 times a week
- RetestAt 3–6 months: compare, adjust, or stop
Most people snack their way to insulin resistance. This gives it a break.
Not medical advice
Discuss everything here with a medical doctor before acting on it — supplements included. Your doctor has your bloodwork and history. We have neither.
02 Why it matters
The snack is the problem.
The default
Three meals, two snacks, a latte, something after dinner. Every one of them raises insulin, and a body with insulin up all day can’t easily reach its fat stores. Diets that cut calories but keep the grazing often leave you hungry, tired, and back where you started.
The evidence
In a controlled feeding trial, men with prediabetes who ate in a six-hour window, with dinner before 3 pm, improved insulin sensitivity and blood pressure without losing weight. A case report from Dr. Jason Fung’s Toronto clinic described three patients with type 2 diabetes who came off insulin with supervised fasting. Three patients, not a trial: it shows what’s possible, not what’s typical.
The catch
In head-to-head trials, fasting usually loses about as much weight as plain calorie cutting, not more. In Krista Varady’s year-long Chicago trial, people eating between noon and 8 pm lost about what calorie counters lost. And if you fast without enough protein, part of what you lose is muscle. Timing helps; it doesn’t replace what you eat.
Knowing what fasting actually does tells you how to do it.
03 How it works
Fasting is when insulin falls.
When you eat, insulin rises and tells your body to store energy. When you stop, insulin falls and your body switches to its reserves: first sugar stored in the liver, then fat. Eat all day and you rarely get to the second part. Fasting is just making sure you do, on a schedule.
- Insulin
- The storage hormone. While it’s high, fat stays locked in. Long, regular gaps between meals keep its average down. That’s the core of Fung’s case for fasting: chronically high insulin feeds insulin resistance, and not eating is the most direct way to bring it down.
- Liver glycogen
- Your short-term sugar store. It runs low somewhere between 12 and 36 hours without food, depending on what you ate and how active you are. After that, the body leans harder on fat.
- Metabolic switching
- The shift from burning glucose to burning fat and making ketones. Researchers Rafael de Cabo and Mark Mattson argue that repeatedly flipping this switch, not just eating less, drives many of fasting’s benefits.
- The body clock
- Your liver, muscle and fat run on a daily clock, and they handle food better early in the day than late at night. Satchin Panda’s lab at the Salk Institute has spent years on this. In his small pilot, people with metabolic syndrome who had been eating across 14 hours or more a day cut to a 10-hour window for 12 weeks; weight, waist, blood pressure and atherogenic lipids came down. No control group, so treat it as a signal, not proof.
- Hunger
- It comes in waves tied to habit, not a rising tide. It usually peaks at your normal mealtimes and passes. Most people find it easier by the second week.
- Muscle
- Fasting doesn’t eat muscle by itself, but not eating enough protein in your window does. Lifting is the signal that tells your body to keep it.
04 The steps
Check. Shrink the window. Add one long fast. Retest.
Check first · Before day 1
Some people shouldn’t fast without a doctor.
- Medicationsthe big one
Insulin, sulfonylureas and other diabetes drugs can drop your blood sugar dangerously when you stop eating. Blood-pressure pills may need adjusting as you lose weight and salt. Ask your doctor before you start, and don’t change a dose on your own.
- Who should waitdoctor first
Pregnancy, breastfeeding, type 1 diabetes, being underweight, a history of eating disorders, gout, kidney disease, or being under 18. Not a hard no for everyone, but not a solo project.
Before you fast
Don’t do extended fasts if you’re on insulin or other diabetes medication, pregnant, breastfeeding, underweight, or have a history of eating disorders, unless your doctor approves.
Measure · Week 0
Get a baseline worth comparing against.
- Weight and waistsame scale, same tape
Waist at the belly button. More than half your height points to visceral fat, the fat fasting draws on first.
- Fasting insulin and glucosemorning, after an overnight fast
Together they give HOMA-IR, a simple insulin-resistance score. Fasting insulin often isn’t covered in Canada. It’s cheap to pay for. If insulin is high, you’re the person this plan was built for.
- HbA1c and lipid panelcontext
Your three-month blood sugar average, triglycerides and HDL. Book them on a normal eating day, not mid-fast.
- Continuous glucose monitortwo weeks
A small sensor on your arm for 14 days shows which meals spike you, how high, and for how long. Repeat every 4–6 months to see the trend. Optional, but it shows you exactly what happens to your blood sugar during a fast, and after you break it.
Shrink the window · Weeks 1–2
Start with the night. Then push breakfast.
Don’t jump straight to long fasts. Move the edges, a little at a time.
- 12 hoursdays 1–4
Nothing after dinner, nothing until 12 hours later. Most of it happens while you sleep. Kill the evening snack first; it’s the easiest win.
- 14 hoursdays 5–9
Push the first meal later. Black coffee, tea or water in the morning. No milk-and-sugar lattes: that’s breakfast.
- Eating window16:8 from week 2, e.g. noon to 8 pm
Eat inside a fixed window and not outside it. Fewer insulin spikes per day, fewer chances to overeat. Earlier windows (say 8 am to 4 pm) have the better trial data for insulin sensitivity, which fits Panda’s body-clock work. Pick the one you’ll actually keep. If 16:8 is a struggle, a steady 10-hour window, the one Panda tested, is a fair place to stop.
- Two or three mealsinside the window
Not a window of continuous grazing. Two proper meals, maybe a third. A window full of snacks misses the point.
Eat properly in the window · Every day
When you eat matters. What you eat matters more.
- Real foodprotein first
Build meals on protein, vegetables and natural fats: fish, meat, eggs, dairy, legumes, nuts. Protein and fibre keep you full and flatten glucose spikes. Fewer meals means each one has to carry more protein. Start every meal with it.
- Sugar and refined carbscut hard
Sugar, sweet drinks, juice, white flour and most packaged snacks. The fastest lever on insulin, blood sugar and triglycerides. A window full of sugar and white flour keeps insulin high anyway, and makes the fasting hours harder.
- Trainingstrength 2–3×/week, cardio 150+ min/week
Lift, and walk briskly or cycle most days. Muscle is where most of a meal’s glucose ends up, so more muscle means more room for it. Cardio makes that muscle more sensitive to insulin. Lifting is what stops a fasting plan from becoming a muscle-loss plan. Train near your eating window if you can.
- Sleep7+ hours
One short night measurably worsens insulin sensitivity, blood sugar and appetite the next day. The cheapest part of the protocol, and the most skipped.
- Alcoholnone while fixing the numbers
It goes straight to the liver, raises triglycerides and adds to liver fat. Less is better; none is best while you’re fixing the numbers.
Go longer · From week 3
One long fast a week.
- 24-hour faststart here
Dinner to dinner. Water, black coffee, tea. You skip breakfast and lunch once. If that feels fine after two or three weeks, try 36.
- 36-hour fastonce a week
Dinner one day, then only water, black coffee or tea until breakfast two days later. A standard protocol in Dr. Fung’s clinic: long enough for insulin to fall and the body to draw on stored fat. A pinch of salt helps with headaches. This is where insulin gets its longest break of the week, and where Fung’s clinic sees most of the change in stubborn cases.
- How to break a fastsmall, then normal
A normal-sized meal built on protein and vegetables. Not a feast. Breaking a long fast with a pile of carbohydrates is the fastest way to feel awful.
- When to stop earlyno medals
Dizziness, palpitations, confusion, or feeling genuinely unwell: eat, and tell your doctor. Hunger and mild irritability aren’t reasons. Feeling faint is.
Retest · Months 3–6
Compare. Adjust. Or stop.
- Same testssame lab, eating day
Weight, waist, fasting insulin and glucose, HbA1c, lipids. If insulin fell and your waist shrank, it’s working.
- Check your musclestrength, not just the scale
If your lifts are going down, you’re under-eating protein or fasting too long. Eat more in the window, or fast less.
- If it isn’t workingbe honest
No change in 3 months usually means the window is full of the wrong food, or the fasting hours aren’t real. Varady’s trials suggest the window works mainly by making you eat less; if it isn’t doing that for you, it isn’t doing much. Some people simply do better on three plain meals with no snacks. That’s a fine answer.
- If the numbers won’t moveyour doctor
Take the before-and-after numbers to your doctor. Whether you need medication is their call. Needing it isn’t failure.
05 The rules
Short list. No exceptions.
Choose
- Water, black coffee and plain tea while fasting
- Protein first when the window opens
- Two or three real meals, not a window of snacking
- Strength training 2–3 times a week
Avoid
- Snacking after dinner
- Sweetened drinks, milky lattes and juice during the fast
- Breaking long fasts with a binge
- Stacking long fasts and hard training on no food
Non-negotiables
- Talk to a medical doctor first if you take any medication, especially for diabetes or blood pressure.
- Never change a medication dose yourself.
- Enough protein to keep your muscle.
- Stop if you feel faint or unwell. Hunger is normal; collapse isn’t.
06 Checkpoints
What to track, and what good looks like.
Track a few numbers before you start and at 3–6 months. The scale is the least useful of them.
| What | Target | How and when |
|---|---|---|
| Waist-to-height | <0.5 | Waist at the belly button divided by height, same units. Monthly. |
| Fasting insulin / HOMA-IR | HOMA-IR under ~1.0 is ideal; over ~2.5 suggests insulin resistance | Fasting glucose (mmol/L) × fasting insulin (µU/mL) ÷ 22.5. Before and at 3–6 months. |
| HbA1c | <6.0% (Canada) · <5.7% (US), and falling | Every 3–6 months if it was high. 6.5% or higher is diabetes. |
| Triglycerides | <1.7 mmol/L (150 mg/dL) | Lipid panel on a normal eating day. Often the first number to fall. |
| Strength | Holding steady or rising | Log your main lifts, or grip strength. Falling strength means you’re losing muscle. |
| How you feel | Steady energy, less hunger by week 3 | If you’re still miserable after a month, change the window or stop. |
Converted values are rounded. Don’t get blood work in the middle of a long fast: fasting can temporarily push LDL and some other numbers up.
07 Where experts disagree
Where the experts don’t agree.
Nobody serious says eating all day, every day, is a good idea. The arguments are about whether the clock does anything that calories don’t, who it suits, and whether short windows are safe.
Does fasting beat simply eating less?
Fasting clinic: Fung
Fasting lowers insulin in a way that eating less but often doesn’t, lets the body reach its fat stores, and is easier for many people than counting.
Body clock: Panda
When you eat matters in its own right. Lining meals up with the body clock, and not eating late into the night, improves metabolism beyond what the calories alone explain.
Fasting trialists: Varady, Liu et al., the TREAT team
In Varady’s trial, the noon-to-8 group cut about as many calories as the counters without being told to, and lost about as much. In Liu’s 12-month trial, adding time restriction to calorie restriction did no better than calorie restriction alone. In TREAT, 16:8 on its own lost no more than three regular meals.
Our read For weight, total intake wins. Fasting is a way of eating less that many people find easier to keep. That’s not a knock: keeping it is the whole game. The clock effect is real in the lab and promising in small trials, but not yet proven to matter much once intake is equal.
Does it cost you muscle?
The TREAT team (UCSF)
Their 16:8 group lost more lean mass from the arms and legs than the control group, a warning that time-restricted eating can eat into muscle.
Muscle-first: Gabrielle Lyon
Muscle is the base of metabolic health, so protein and resistance training come first. Get those right and the eating window is a detail.
Our read Both are right. Fasting plus low protein and no lifting costs muscle. Fasting plus enough protein and resistance training largely doesn’t. That’s why both are in this plan.
Is fasting different for women?
Caution: Stacy Sims
Much of the fasting evidence comes from men or sedentary people. Active women before menopause are more sensitive to low energy intake, and long fasts on top of hard training can disrupt hormones. Eat around training, especially protein.
Fasting clinics: Fung
His clinic uses fasting with women as well as men. Insulin resistance is the target either way; adjust the length of the fast rather than ruling it out.
Our read If you’re a woman who trains hard, keep fasts shorter, don’t train hard fasted, and eat protein soon after. If your cycle changes, back off.
Do short eating windows raise heart risk?
Zhong and colleagues
In US survey data on about 20,000 adults, eating within less than eight hours a day was linked to a higher risk of dying from heart disease.
Critics, including fasting researchers
The data came from a couple of days of self-reported eating, not people deliberately following a fasting plan. People who eat in short windows may be shift workers, unwell, or poor. It’s an association, not cause.
Our read Observational and weak, but not nothing. It’s a reason to protect muscle, eat real meals, and not treat the shortest window as the best.
08 Limits
What no plan fixes.
It’s a tool, not magic
Fasting won’t outrun a window full of ultra-processed food, bad sleep and no training. It works best on top of the basics, not instead of them.
Not for everyone
If you have a history of disordered eating, fasting can feed it. If you’re pregnant, breastfeeding, underweight or on glucose-lowering medication, it’s your doctor’s call, not this page’s.
Medications and conditions
Some drugs push weight and blood sugar up regardless of when you eat. Thyroid problems, steroid use and hormonal conditions need diagnosing, not out-fasting.
The plan gives insulin a break. It doesn’t replace food quality, sleep or your doctor.
09 Resources
Worth your time.
The Complete Guide to Fasting
The practical manual: how to run 16-hour, 24-hour and 36-hour fasts, and what goes wrong.
The Obesity Code
The case that insulin, not calories, sets your weight, and why eating less often helps.
The Circadian Code
The body-clock case for eating in a consistent daytime window, from the scientist who ran many of the time-restricted eating studies.
Effects of intermittent fasting on health, aging, and disease
The best single review of what fasting does in the body, and how strong the evidence is.
Time-restricted eating without calorie counting for weight loss in a racially diverse population
A year-long randomized trial of noon-to-8 eating against calorie counting. The honest answer to “does it work?”: about as well, without the counting.
10 Questions
Questions, answered plainly.
Does black coffee break a fast?
No, not in any way that matters. Black coffee and plain tea barely touch insulin. Milk, sugar, syrups and “bulletproof” butter coffee are food.
Which is best: 16:8, 18:6, or OMAD?
The one you can keep. Longer daily fasts aren’t clearly better, and very short windows make it hard to eat enough protein. Start at 16:8 and add one longer fast a week. If that’s too much, a consistent 10-hour daytime window still has trial support.
Will fasting put me into “starvation mode”?
Not in a day or two. Short fasts don’t crash your metabolism. Chronic under-eating with low protein and no training can, partly by costing you muscle. That’s why this plan protects it.
Can I work out while fasting?
Walking, yes. Hard training on an empty stomach is fine for some people and poor for others, especially women before menopause. If your performance drops, eat before or soon after.
How fast will I lose weight?
Usually about as fast as any diet that cuts the same amount of food. In Varady’s trial, noon-to-8 eating and calorie counting lost about the same over six months. Results vary a lot between people. Insulin and waist often move before the scale does.
I take diabetes medication. Can I fast?
Only with your doctor actively involved. Fasting on insulin or sulfonylureas without adjusting the dose can cause dangerous lows. Done with supervision, some people reduce or come off medication. Never on your own.
11 Sources
Where this comes from.
Experts drawn on
- Jason Fung, MD — Nephrologist, Toronto. Author of The Obesity Code and The Complete Guide to Fasting.
- Krista Varady, PhD — Nutrition scientist, University of Illinois Chicago. Has run many of the randomized trials of alternate-day fasting and time-restricted eating.
- Satchin Panda, PhD — Professor, Salk Institute. Circadian biologist behind much of the time-restricted eating research; author of The Circadian Code.
- Mark Mattson, PhD — Neuroscientist, formerly National Institute on Aging; adjunct professor, Johns Hopkins. Fasting and metabolic switching research.
- Stacy Sims, PhD — Exercise physiologist and nutrition scientist. Female physiology, training and fueling.
- Gabrielle Lyon, DO — Physician; founder of muscle-centric medicine. Protein and muscle as the foundation of metabolic health.
Sources
- Effects of intermittent fasting on health, aging, and disease. New England Journal of Medicine, 2019.
- Early time-restricted feeding improves insulin sensitivity, blood pressure, and oxidative stress even without weight loss in men with prediabetes. Cell Metabolism, 2018.
- Therapeutic use of intermittent fasting for people with type 2 diabetes as an alternative to insulin. BMJ Case Reports, 2018.
- Calorie restriction with or without time-restricted eating in weight loss. New England Journal of Medicine, 2022.
- Effects of time-restricted eating on weight loss and other metabolic parameters in women and men with overweight and obesity: the TREAT randomized clinical trial. JAMA Internal Medicine, 2020.
- Clinical management of intermittent fasting in patients with diabetes mellitus. Nutrients, 2019.
- Association of eating duration less than 8 h with all-cause, cardiovascular, and cancer mortality. Diabetes & Metabolic Syndrome: Clinical Research & Reviews, 2025.
- Intermittent fasting study sparks debate over increases in CV mortality. TCTMD, 2024.
- Time-restricted eating without calorie counting for weight loss in a racially diverse population: a randomized controlled trial. Annals of Internal Medicine, 2023.
- Ten-hour time-restricted eating reduces weight, blood pressure, and atherogenic lipids in patients with metabolic syndrome. Cell Metabolism, 2020.
Not medical advice
Discuss everything here with a medical doctor before acting on it — supplements included. Your doctor has your bloodwork and history. We have neither.