Quick Answer
Weight loss myths are common, and most fail when checked against trials and health agency guidance. A large US trial found low-fat and low-carb diets gave similar 12-month results (5.3 kg versus 6.0 kg). Reviews of eating frequency show no clear weight advantage to many small meals. Little scientific evidence shows weight-loss supplements work. The CDC and NHS describe 1 to 2 pounds (0.5 to 1 kg) a week as a steady pace, not a target.
Below, each of the weight loss myths gets the best available evidence and plain guidance. For wider context, see our guide to sustainable weight loss tips and our checklist for spotting fad diets.
Ten Weight Loss Myths at a Glance
| Myth | What the evidence shows | Verdict |
|---|---|---|
| You must cut all carbs | Low-carb and low-fat diets gave similar 12-month loss in a 609-person trial | Not supported |
| Fat in food makes you fat | Same trial: no meaningful gap between low-fat and low-carb groups | Not supported |
| Skipping meals speeds loss | NHS advises against it; skipped meals can lead to more snacking | Not supported |
| Many small meals boost metabolism | 16 trials: no clear weight difference by eating frequency | Not supported |
| Cardio is the only way | Both cardio and strength work count; we found no source ranking cardio alone first | Not supported |
| You cannot spot-reduce fat | One small 2023 trial reported trunk-fat loss from abdominal exercise | Contested |
| Diet pills are the answer | NIH: little scientific evidence that supplements work | Not supported |
| Late-night eating causes gain | Small, mixed studies; no firm conclusion | Unproven |
| Faster loss is better | CDC: steady loss is more likely to be kept off | Not supported |
| Water with meals causes gain | We found no source supporting this | Not supported |
Sources: NIHR summary of the DIETFITS trial, eating frequency meta-analysis, NHS, CDC and NIH Office of Dietary Supplements.
Weight Loss Myths About Carbs and Fat
Among weight loss myths, the idea that you must cut all carbohydrate or all fat is common. The DIETFITS trial tested this. It randomised 609 adults with overweight or obesity to a low-fat or low-carbohydrate diet. At 12 months, the low-fat group lost about 5.3 kg and the low-carb group about 6.0 kg. The 0.7 kg gap was not statistically significant (NIHR).
Neither genetics nor insulin response predicted who did better on which diet. As a result, the best pattern is usually the one you can keep. Our guides to macronutrients and balancing protein, carbs and fats explain what each does in the body.
Weight Loss Myths About Meals and Metabolism
The NHS tells people not to skip meals, because hunger may lead to more snacking (NHS). It also advises against losing weight suddenly with diets. Our page on skipping meals and weight loss covers this in more detail.
The opposite claim is that eating many small meals keeps metabolism running. A 2023 meta-analysis pooled 16 trials of at least two weeks. It compared three or fewer meals a day with four or more. Weight change did not clearly differ (mean difference -0.62 kg, 95% CI -2.76 to 1.52). However, certainty was very low. Also, 15 of 16 trials had a high risk of bias (meta-analysis).
So neither claim has strong support. See the research on eating frequently and the role of metabolism in weight loss. Very low intake carries its own risks, including nutrient gaps, so check with a clinician first.
Exercise and Spot Reduction: A Myth With a Twist
Cardio does use energy, but it is not the only useful activity. Strength work and everyday walking count too. Our guide on how walking can help you lose weight shows a low-barrier option.
Of all weight loss myths, spot reduction is more complicated than most sites admit. A 2023 randomised trial gave 16 overweight men a 10-week abdominal endurance programme, four days a week. They lost about 1,170 g (7%) of trunk fat, while a treadmill-only group showed no change. The between-group difference was 697 g (3%). Both groups lost similar total fat (trial abstract).
That is a very small study in one group. Therefore it does not overturn the general view that fat loss is spread across the body. Still, the confident claim that you can never lose fat locally is stronger than the evidence.
Weight Loss Myths About Pills and Water
The NIH Office of Dietary Supplements says there is little scientific evidence that weight-loss supplements work. Makers rarely test them in people, and studies tend to be small and short. Some products are adulterated with prescription drugs not listed on the label. The FDA does not approve supplements before they are sold (NIH ODS).
Mayo Clinic content links some supplements to liver damage. It adds that ephedra was banned over heart and blood pressure risks (Mayo Clinic health library). Prescription medicines are a separate topic, covered in medical weight loss options and Alli weight loss pills.
On water, we found no source showing that drinking with meals causes weight gain. In one 12-week trial summary, adults who drank 500 ml of water before meals lost about 2 kg more than a diet-only group (trial report). The NHS suggests swapping sugary drinks for water. See also how drinking water affects weight loss.
Late-Night Snacks and Fast Loss
Eating late is often blamed for gain. A review of small studies found mixed results. One favoured night eating, two favoured earlier eating, and two were inconclusive (Examine.com summary). It is an aggregator, so treat it as a guide only. Total intake and sleep matter too, as shown in how sleep affects weight loss.
On speed, the CDC says a gradual pace of about 1 to 2 pounds a week makes weight loss more likely to last (CDC). The NHS gives 0.5 to 1 kg a week. These describe typical steady loss, not a target. Our page on losing a pound a day explains why faster is rarely better. Afterwards, see maintaining weight loss.
Why Published Answers Disagree
Weight loss myths pages often sound certain, yet the underlying studies are small. The spot-reduction trial had 16 people. The night-eating studies were short and varied in design. The meal-frequency trials were mostly at high risk of bias.
Averages also hide individuals. In DIETFITS, mean loss was similar across diets, but individual results ranged widely. In short, a myth can be wrong on average and still hold for one person.
Finally, comparison groups matter. A fasting or exercise group beating a control that did nothing is not the same as beating a sensible alternative. Our intermittent fasting evidence review shows this clearly.
Evidence Summary for Common Claims
| Claim | Where it stands | Reader guidance |
|---|---|---|
| Skipping meals drops metabolism sharply | Not supported | Sources reviewed do not show this. The NHS still advises against skipping meals. |
| Many small meals keep metabolism running | Not supported | Trials show no clear weight difference. Choose a pattern you can keep. |
| Starvation mode makes weight loss impossible | Overstated | Loss may slow, but we found no source showing it stops. Very low intake risks nutrient gaps. |
| You cannot spot-reduce fat | Contested | One small trial disagrees. Expect fat loss across the body. |
| Supplements give a useful boost | Little evidence | Talk to a clinician before taking any, especially alongside medicines. |
| Late-night eating causes gain | Unproven | Studies are small and mixed. Overall intake still matters. |
| Strength training greatly raises metabolism | Size unverified | We could not verify a figure. Do it for strength and health. |
| Water with meals causes gain | Not supported | No source found. Water has no energy content. |
Safety: When to Talk to a Clinician First
Diet changes are not right for everyone. Speak to a doctor or dietitian first if you take prescription medicines, live with diabetes, or have a heart or kidney condition. Tell them about any supplement, since some interact with medicines.
If you are pregnant, NHS guidance says not to diet or try to lose weight, because you may not get enough nutrients (NHS trust guidance). Children and teenagers should only change diet with a GP or paediatrician.
Weight loss myths can feed disordered eating. Warning signs include rigid food rules and constant preoccupation with food or body (Duke Psychiatry). In the US, the National Alliance for Eating Disorders helpline is 866-662-1235 (weekdays), per the Alliance. The old NEDA helpline is disconnected. Call or text 988 in a crisis (SAMHSA). In the UK, Samaritans is free on 116 123. See also emotional eating causes and coping.
Weight Loss Myths FAQ
No. In a 609-person trial, low-carb and low-fat diets gave similar results at 12 months, about 6.0 kg versus 5.3 kg.
The NHS advises against it, because hunger can lead to more snacking. Evidence for a benefit is weak.
A meta-analysis of 16 trials found no clear weight difference between eating three or fewer meals and four or more. Certainty was very low.
Mostly no, but one small 2023 trial of 16 men reported more trunk-fat loss with abdominal exercise. It needs larger replication.
The NIH says there is little scientific evidence that they work. Some products contain undeclared drugs. Ask a clinician first.
Studies are small and mixed. Total intake, sleep and overall habits seem to matter more than clock time.
The CDC says gradual, steady loss of about 1 to 2 pounds a week is more likely to be kept off. NHS gives 0.5 to 1 kg.
We found no source supporting this. One trial summary found pre-meal water linked to about 2 kg extra loss over 12 weeks.
People who are pregnant, under 18, living with diabetes, on regular medicines or with an eating disorder history should speak to a clinician first.
Related Reading
- Counting calories: how accurate is it, and who should skip it
- Intermittent fasting for weight loss: what the studies show
- Sustainable weight loss tips that last
- How to spot a fad diet
Sources
- CDC: Steps for Losing Weight
- NHS: Tips to help you lose weight
- NIH Office of Dietary Supplements: Dietary Supplements for Weight Loss (updated March 2021)
- NIHR Evidence: Low-fat or low-carbohydrate diets seem just as effective for weight loss
- Effects of eating frequency on body composition and cardiometabolic health: systematic review and meta-analysis (2023)
- Abdominal aerobic endurance exercise reveals spot reduction exists: randomised trial (Physiological Reports, 2023)
- Mayo Clinic health library: Dietary supplements for weight loss
- Examine.com: Does eating at night make weight gain more likely (aggregator)
- NHS Derbyshire Family Health Service: Managing your weight during pregnancy
- Site pages: sources cited, fact-checking policy and editorial process
Written and fact-checked by the HealthCoachJP editorial team. No clinician has reviewed this article. See our sources cited page. Last reviewed and rewritten October 2026.
Medical disclaimer: this article is general information, not medical advice. Talk to a doctor or registered dietitian before changing your diet or taking any supplement.
