Common Nutrition Myths We Revisit After 40

Nutrition advice ages unevenly. Some principles — eat a variety of whole foods, prioritize protein and fibre, moderate alcohol — have held up across decades of research. Others, repeated often enough that they feel like settled fact, turn out to rest on thin or outdated evidence. For men past 40 making real decisions about how to eat, it is worth revisiting a few of the claims that circulate most persistently in gyms, group chats and supplement marketing.

Myth: "Your Metabolism Shuts Down After 40"

Resting metabolic rate does decline with age, but the magnitude is more modest than the phrase "shuts down" implies, and a large 2021 study published in Science using doubly labelled water measurements across thousands of participants found total daily energy expenditure remains relatively stable from roughly age twenty to sixty when adjusted for body composition, declining more noticeably only after sixty. The weight gain many men experience in their forties is more consistently explained by reduced activity levels and muscle loss than by a dramatic metabolic slowdown.

Myth: "Carbohydrates Become the Enemy With Age"

Carbohydrate tolerance can shift with reduced activity and increased insulin resistance, but this is a consequence of lifestyle factors rather than an inevitable feature of aging itself. Men who maintain regular resistance and aerobic training generally preserve glucose tolerance far better than sedentary peers of the same age. Blanket avoidance of an entire food category is rarely the most useful response; activity level and overall dietary pattern matter more than any single macronutrient.

"Most nutrition advice that ages well is specific. Most that ages poorly is absolute."

Myth: "Supplements Can Substitute for a Poor Diet"

The supplement industry markets heavily to men over 40 concerned about declining energy or muscle mass. The evidence for most over-the-counter supplements marketed this way is considerably weaker than for the basics they are positioned to replace — adequate protein, sufficient sleep and regular resistance training. A small number of supplements (creatine and vitamin D in populations with documented deficiency, for example) have reasonably strong evidence in specific contexts, but none substitute for foundational habits.

Myth: "Skipping Breakfast Ruins Your Metabolism"

Intermittent fasting research has not found consistent evidence that meal timing alone — independent of total calorie and nutrient intake — meaningfully damages metabolic health in otherwise healthy adults. Some men find structured eating windows easier to maintain consistently; others do better with more frequent smaller meals. The deciding factor in most studies is whether the approach is sustainable for the individual, not whether it follows a particular timing rule.

What Tends to Hold Up

Across the nutrition literature our contributing dietitian reviews most often, a short list of principles recurs with unusual consistency: adequate protein distributed across meals, sufficient fibre from vegetables, legumes and whole grains, limited intake of ultra-processed foods high in added sugar, and moderate alcohol consumption. None of these claims are new or exciting, which is part of why they are reliably overshadowed by more dramatic alternatives — but they are also the recommendations that have survived the most scrutiny.

Readers interested in how these principles intersect with training recovery may also want to read our piece on strength training as a long-term investment, and those curious about how eating patterns relate to hormonal markers can explore our hormonal health pillar.

This article reflects a review of nutrition research current as of its publication date and does not constitute individualized dietary advice. Readers with specific medical or nutritional needs should consult a registered dietitian. See our medical disclaimer.