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Nutrition myths, checked
18 common claims with a verdict, what is actually known, why the myth persists, and the arithmetic that settles it — computed live from the food and exercise database.
How a claim is judged here
Four verdicts, and one of them is used deliberately often. False means the claim states a mechanism that does not exist. Mostly false means the headline is wrong but something real sits underneath it. It depends means the honest answer changes with who is asking, or the evidence is genuinely split — that verdict is not a hedge, it is a finding. True means what it says.
Where arithmetic can settle a claim, the arithmetic is done on the page rather than described. Those numbers are computed when the page loads, from the same food database behind every calorie page on this site and the same MET table behind every exercise page, so they cannot drift out of step with their source. No study is cited by name anywhere in this section: where a position belongs to guideline bodies, it is attributed to guideline bodies.
The claims
| Claim | Verdict | The short answer |
|---|---|---|
| Eating after 8pm makes you gain weight. | Mostly false | The clock does not add calories. What the clock does is change how much you eat and how well you sleep — and those are real effects with an ordinary explanation. |
| Breakfast is the most important meal of the day — skip it and you will gain weight. | It depends | Breakfast eaters do tend to be leaner. Adding breakfast to someone who was skipping it does not reliably make them leaner. Those two sentences are both true, and the gap between them is where the myth lives. |
| Detox teas flush toxins out of your body and help you lose weight. | False | No product on this market names the toxin it removes or measures it before and after. The weight that moves is water and gut contents, and much of it moves because of a laxative. |
| Some foods take more energy to digest than they contain, so eating them burns calories. | False | Digestion costs a fraction of a food's energy, not more than all of it. Even at the most generous figure ever measured for a whole food, the classic "negative calorie" list still leaves you ahead. |
| Do enough crunches and the fat over your abs will go. | False | Training a muscle builds that muscle. It does not preferentially withdraw fat from the skin above it. Where fat leaves from is set by genetics, sex and hormones, not by which exercise you chose. |
| The more you sweat, the more fat you are burning. | False | Sweat is a cooling system, not an exhaust pipe. It measures how hot you are, not how hard you worked — and every gram of it comes back the moment you drink. |
| Do not eat carbohydrates after 6pm. | False | The same slice of bread has the same energy at 18:01 as at 17:59. This rule works, when it works, by deleting a category of food from the part of the day when most snacking happens. |
| If you stop training, your muscle turns into fat. | False | Muscle and fat are different tissues. One cannot become the other any more than a bone can become blood. What happens is two separate changes that arrive at the same time and look like one. |
| Celery has negative calories: you burn more chewing it than it contains. | False | Celery is the poster food for a claim that has never been measured in anyone. The arithmetic below uses the most generous digestion cost ever recorded for a whole food and celery still comes out positive. |
| You must drink eight glasses of water a day. | It depends | The target is real in spirit and wrong in the specifics: it is the wrong volume, it ignores food and every other drink, and it is the same number for a 50 kg office worker and a 100 kg roofer in August. |
| Fresh vegetables and fruit are always more nutritious than frozen. | Mostly false | Frozen produce is picked ripe and blanched within hours. "Fresh" produce is often picked early and then spends a week in transport and another in your fridge. The comparison the myth imagines is rarely the comparison you are making. |
| Brown sugar, raw sugar and honey are healthier than white sugar. | Mostly false | Brown sugar is white sugar with a little molasses added back. The mineral content that gets advertised is real, present in trace amounts, and would require an absurd quantity of sugar to matter. |
| Gluten-free food is healthier, even if you do not have coeliac disease. | False | For the roughly 1% of people with coeliac disease, gluten-free is medically necessary and non-negotiable. For everyone else, the label describes what was removed, and the arithmetic below shows what usually replaces it. |
| Microwaving destroys the nutrients in food. | False | Every cooking method costs some nutrients. Microwaving usually costs the fewest, because nutrient loss tracks heat, time and water — and a microwave uses less of all three. |
| Egg yolks raise your cholesterol, so eat only the whites. | It depends | This is the one on the list where the evidence is genuinely mixed and honest experts still disagree. What has clearly changed is the old assumption that dietary cholesterol maps straight onto blood cholesterol for everyone. |
| My metabolism is broken — that is why I cannot lose weight. | Mostly false | Metabolic adaptation to weight loss is real, measurable and frustrating. It is also far smaller than the gap between what people believe they eat and what they actually eat. |
| Your metabolism slows down after 40 and that is why you gain weight. | Mostly false | The age term in every standard energy equation is small, and the arithmetic below prints it. The change people actually experience between 25 and 45 is mostly muscle and movement, both of which are addressable. |
| Eating six small meals a day keeps your metabolism stoked. | False | The energy cost of digesting food is a percentage of the food, not a fee per meal. Splitting the same day into more meals divides the same total into more pieces — the arithmetic below does it both ways and gets the same answer. |
What this page will not do
- Invent a study. Not one citation on these pages names a paper, because naming papers we have not verified line by line would be worse than naming none.
- Pick a side where the evidence is split. Egg yolks and non-coeliac gluten sensitivity both get "it depends", because that is what the evidence supports today.
- Give medical advice. Coeliac disease, raised cholesterol, diabetes and thyroid disease all appear on these pages, and every one of them points at a clinician rather than at a conclusion.
- Print a number the database does not hold. Where a comparison needs a nutrient TempoLife does not store — cholesterol per egg, vitamin C after cooking — the page says so and argues in words instead.
Source: USDA FoodData Central (SR Legacy) via the TempoLife food database, and the 2011 Compendium of Physical Activities for MET values · checked 2026-09-02
Frequently asked questions
Why is "it depends" a verdict?
Because for some claims it is the accurate one. Forcing a yes or no onto a question where good researchers still disagree would be a worse error than the myth being checked.
Where do the calculations come from?
Food figures come from the TempoLife food database, which carries USDA FoodData Central SR Legacy rows. Energy cost of movement uses the ACSM equation with MET values from the 2011 Compendium. Resting energy uses Mifflin-St Jeor. All three are printed on the pages that use them.
Is a myth page ever wrong?
It can be. Nutrition evidence moves, and a verdict that was right in 2020 may not be right in 2030 — dietary cholesterol is the standing example. Corrections are made on the page rather than quietly.
Weekly research digest · Glossary · All calculators
Check a claim against your own numbers
Most of these arguments end at "it depends on your total intake". TempoLife measures that total — meals, steps, sleep and weight in one timeline — so the question stops being theoretical.