Nutrition Science Myths That Just Won't Die

The idea that carbohydrates are uniquely responsible for weight gain became mainstream during the low-carb diet wave, but the physiology doesn't support a carb-specific blame. Body weight is largely governed by overall energy balance — calories consumed versus calories expended. Research published in journals including Cell Metabolism and reviews by the National Institutes of Health have found that when calories and protein are held equal, low-fat and low-carbohydrate diets produce similar weight outcomes. The quality of carbohydrates matters considerably: whole grains, legumes, and vegetables behave very differently in the body than refined sugars and white flour. Cutting heavily processed carbs can support better health — but that benefit is about food quality, not the macronutrient category itself. For a deeper look at dietary fiber — the carbohydrate component most Americans fall short on — see dietary fiber and what the science says.

The eight-glasses-a-day guideline is one of nutrition's most durable myths. It appears to trace back to a 1945 U.S. Food and Nutrition Board recommendation that was widely misread — the original text noted that most of the recommended fluid intake is contained in food. The Institute of Medicine (now the National Academy of Medicine) sets general adequate intake levels for total water, which include fluids from all beverages and food sources combined — not eight glasses of plain water. Thirst is a reliable hydration cue for most healthy adults. Urine color (pale yellow generally indicates adequate hydration) is a more individualized and practical guide than a fixed glass count.

The low-fat diet movement of the 1980s and 1990s entrenched the idea that eating fat causes weight gain, but evidence since then has substantially revised that picture. Dietary fat is calorie-dense — at 9 calories per gram compared to 4 for carbohydrates and protein — so high-fat foods can make it easier to overconsume calories. But the fat itself is not metabolically problematic in moderate amounts. In fact, unsaturated fats found in foods like olive oil, avocados, nuts, and fatty fish are associated with cardiovascular benefits in numerous large studies. Trans fats (now largely removed from the food supply) and excess saturated fat carry more documented risk. The low-fat food trend also had an unintended consequence: manufacturers replaced fat with added sugar, which may have worsened metabolic health outcomes. See our coverage of eating fat makes you fat and other persistent myths for more context.

The claim that breakfast is metabolically essential has been repeated so often it feels like settled science — but the research is more nuanced. Several large randomized controlled trials, including one published in The BMJ, found that recommending breakfast for weight loss did not produce the expected results and that skipping breakfast did not meaningfully slow resting metabolism in healthy adults. Intermittent fasting approaches, which often involve skipping breakfast, have shown neutral-to-positive outcomes in some populations. That said, breakfast may benefit children, athletes, and people with blood sugar regulation concerns. The key variable is what a person eats across the full day, not the timing of the first meal.

Organic food carries associations with health and purity, which has led many consumers to assume it is nutritionally superior. However, systematic reviews — including a widely cited 2012 analysis from Stanford University published in the Annals of Internal Medicine — found little evidence that organic foods are significantly more nutritious than their conventional counterparts in terms of vitamins, minerals, and other nutrients. Pesticide residue differences do exist, though regulatory agencies set limits for conventional produce based on safety thresholds. Whether those residue differences translate to measurable health outcomes in the general population remains an open question in research. Choosing organic may be a reasonable personal preference, but the assumption that it delivers substantially better nutrition is not well-supported by current evidence.

Concern about protein and kidney health stems from the legitimate fact that people with existing chronic kidney disease (CKD) are often advised to moderate protein intake, because impaired kidneys struggle to process nitrogen waste produced during protein metabolism. However, this clinical recommendation has been incorrectly generalized to healthy individuals. Studies in people without kidney disease — including those following high-protein diets — have not demonstrated kidney damage or accelerated decline in kidney function. Major nutrition bodies, including the Academy of Nutrition and Dietetics, note that higher protein intake is safe for healthy adults. Anyone with a history of kidney issues should discuss dietary protein with their nephrologist or physician before making changes. For a broader evidence review, see what the science actually supports about protein intake.