Most of the nutrition advice that gets repeated at dinner tables and in social media posts is either outdated or was never backed by strong evidence in the first place. Several widely believed claims about food, from “carbs make you fat” to “eating late causes weight gain,” fall apart when tested in controlled studies. Here are the most persistent nutrition myths and what the science actually shows.
Sugar Makes Kids Hyperactive
This is one of the most confidently repeated nutrition myths in existence, and it has been thoroughly debunked. A meta-analysis pooling 23 controlled studies found that sugar does not affect behavior or cognitive performance in children. Across 14 different ways of measuring behavior, including direct observation and academic testing, none showed a statistically significant effect from sugar consumption.
So why do so many parents swear by it? The likely explanation is expectancy bias. When parents believe sugar causes hyperactivity, they interpret normal kid energy (especially at birthday parties and holidays, where sugar happens to be present) as confirmation. Studies that told parents their child had consumed sugar, when the child actually hadn’t, found those parents rated their child’s behavior as more hyperactive. The setting drives the perception, not the sugar.
Carbs Cause Weight Gain
Carbohydrates have been treated as the villain of weight loss for decades, but the relationship is far simpler than most diet books suggest. Weight change comes down to overall energy balance. When researchers compare low-carb and low-fat diets matched for total calories, the differences in fat loss are minimal.
There is a more nuanced version of this claim called the carbohydrate-insulin model, which argues that carbs uniquely promote fat storage by spiking insulin. Among the longer controlled feeding studies (lasting more than 2.5 weeks), low-carb diets did show a small metabolic advantage of roughly 50 extra calories burned per day for every 10% reduction in carbohydrate intake. That’s real but modest, equivalent to about half a banana’s worth of energy. It does not mean carbs inherently cause weight gain. Whole grains, fruits, and legumes are carbohydrate-rich foods consistently linked to healthy body weight in large population studies.
Eating Late at Night Makes You Fat
This one is more complicated than a simple true or false. The traditional debunking says “a calorie is a calorie regardless of when you eat it,” but newer evidence suggests meal timing does matter, at least partly.
In a cohort of over 1,200 people, those who consumed 48% or more of their daily calories at dinner were more than twice as likely to be obese at six-year follow-up, even after adjusting for total calorie intake and physical activity. A separate study of 239 participants found a similar doubling of obesity risk for people eating a third or more of their calories in the evening. Animal studies have shown weight gain when meals are shifted to the rest phase of the circadian cycle, even when calorie intake is held constant.
The mechanism likely involves your body’s internal clock. Metabolism, insulin sensitivity, and the way your body processes nutrients all fluctuate throughout the day. That said, the biggest driver of weight change remains how much you eat overall. Timing appears to be a secondary factor, not the primary one.
Eggs Are Bad for Your Heart
For years, eggs were treated as a cholesterol bomb to be avoided. The concern was straightforward: eggs are high in dietary cholesterol, and high blood cholesterol raises heart disease risk. But the link between cholesterol you eat and cholesterol in your blood is weaker than most people assume.
A meta-analysis of metabolic ward studies found that eliminating 200 mg of dietary cholesterol per day (roughly one large egg) lowered blood cholesterol by only about 0.13 mmol/L. That’s a small shift. The far bigger influence on blood cholesterol is saturated fat intake. Replacing saturated fats with unsaturated fats had roughly four to five times the cholesterol-lowering effect of cutting dietary cholesterol alone. For most people, eating an egg a day has a negligible impact on heart disease risk. The toast you butter alongside it likely matters more.
High-Protein Diets Damage Your Kidneys
This myth has a grain of truth buried inside it. For people who already have kidney disease, high protein intake can accelerate the decline in kidney function. But for healthy adults, the evidence tells a different story.
In the OmniHeart trial, 164 healthy adults ate a diet where protein made up 25% of calories (compared to a standard 15%). The higher-protein diet increased their kidney filtration rate by about 4 mL/min. This reflects the kidneys working harder, a response called hyperfiltration. In people with damaged kidneys, that extra workload is harmful. In people with healthy kidneys, it appears to be a normal adaptive response, similar to how your heart rate rises during exercise without damaging your heart.
Whether decades of high protein intake could eventually cause kidney problems in otherwise healthy people remains genuinely uncertain. But the blanket claim that protein damages kidneys is not supported by evidence in people without pre-existing kidney conditions.
You Need a Detox or Cleanse
Your body already runs a sophisticated detoxification system, and it operates 24 hours a day without juice fasts or supplement protocols. The liver uses a two-phase enzyme system to process and neutralize toxins. Phase I enzymes (the cytochrome P450 family) break down harmful substances through chemical reactions like oxidation. Phase II enzymes then attach molecules like glucuronic acid to these byproducts, making them water-soluble so your kidneys can filter them into urine or your liver can dump them into bile for elimination through your digestive tract.
This system handles everything from alcohol to environmental pollutants to the normal waste products of your own metabolism. No commercial cleanse has been shown in clinical trials to improve on what these organs already do. Certain foods, particularly cruciferous vegetables and other plants rich in protective compounds, can support the activity of these enzyme pathways. But that’s an argument for eating well consistently, not for a three-day juice cleanse.
Everyone Should Go Gluten-Free
Gluten-free diets are essential for people with celiac disease, which affects about 1% of the population. There is also a condition called non-celiac gluten sensitivity, which is thought to be more common than celiac disease, though its exact prevalence is still debated. For people in these groups, avoiding gluten meaningfully reduces symptoms.
For everyone else, going gluten-free provides no demonstrated health benefit and may actually work against you. Whole wheat and other gluten-containing grains are significant sources of fiber, B vitamins, and minerals. Many gluten-free packaged products compensate for texture and flavor by adding extra sugar, fat, and refined starches. Interestingly, some people who believe they’re sensitive to gluten actually react to FODMAPs, a group of fermentable carbohydrates found in wheat but also in dozens of other foods. An international panel of researchers established diagnostic criteria for gluten sensitivity that specifically requires ruling out FODMAP intolerance first.
Multivitamins Prevent Disease
Many people take a daily multivitamin as nutritional insurance, assuming it lowers their risk of cancer or heart disease. The U.S. Preventive Services Task Force reviewed the available evidence and concluded it is insufficient to determine whether multivitamins prevent cardiovascular disease or cancer in healthy, non-pregnant adults. That’s not a recommendation against taking them. It means that after examining all the studies, the panel could not find clear evidence of benefit for disease prevention.
Multivitamins can fill genuine nutritional gaps for people with restricted diets or specific deficiencies. But taking one does not compensate for a poor diet, and the assumption that more vitamins equals better health has never been confirmed in large trials of generally healthy people. The nutrients in whole foods come packaged with fiber, fats, and thousands of other compounds that interact in ways a pill cannot replicate.