Nutrition Myths: What Chemistry Says

Nutrition advice changes quickly, and a lot of it spreads through social media faster than evidence can keep up. Some claims are half-true, some are outdated, and some misunderstand basic chemistry. This guide takes ten common nutrition myths and looks at what the molecules actually do. It isn’t personal dietary advice — for that, talk to a doctor or registered dietitian — but it should help you judge the next claim you see.

Myth 1: “A calorie is not a calorie”

What chemistry says: a calorie is a calorie — it’s simply a unit of energy (1 kcal = 4.184 kJ). When food is burned completely in a bomb calorimeter, the heat released is its gross energy. The body doesn’t extract all of it: some is lost in faeces and urine, which is why food labels use slightly lower “metabolisable energy” values, roughly 17 kJ g⁻¹ for carbohydrate and protein, 37 kJ g⁻¹ for fat and 29 kJ g⁻¹ for alcohol.

What the saying really points to is that foods with the same energy have different effects. Protein takes more energy to digest and process than fat; fibre-rich foods are more filling; some energy in whole nuts escapes digestion because cell walls aren’t fully broken down. So the energy is the same unit, but the body’s response to different foods varies.

Myth 2: “Eating carbs at night makes you gain weight”

What chemistry says: the body doesn’t have a clock-controlled switch that turns evening carbohydrates into fat. Weight change over time depends mostly on total energy in versus energy out across days and weeks. Glucose eaten in the evening is still used for energy or stored as glycogen, just like glucose eaten at lunch (see what happens to sugar in your body).

There is some research on meal timing and body clocks — for example, insulin sensitivity tends to be a little lower in the evening — but the effects are modest compared with overall diet. Late-night snacking is often a problem simply because it adds extra food.

Myth 3: “Celery has negative calories”

What chemistry says: the idea is that digesting celery takes more energy than it provides. Celery is about 95 % water and very low in energy — around 60–70 kJ per 100 g. The energy used to digest food (the thermic effect) is typically around 5–10 % of the food’s energy for carbohydrate-rich foods. So digesting 100 g of celery might use a few kilojoules, not more than it provides. It’s a great low-energy food, but not a negative one.

Myth 4: “Sea salt and pink salt are healthier than table salt”

What chemistry says: all of them are mostly sodium chloride, NaCl — typically around 95–99 % by mass. Sea salt and Himalayan pink salt contain small amounts of other minerals (the pink colour comes from traces of iron oxide), but the quantities are too small to matter nutritionally. Gram for gram, they contain about the same sodium as table salt (see sodium).

One real difference: table salt is often iodised, with potassium iodide or iodate added. Iodine is essential for thyroid hormones, and iodised salt has greatly reduced iodine deficiency worldwide. Switching entirely to non-iodised specialty salts can remove this source.

Myth 5: “MSG is a dangerous chemical”

What chemistry says: monosodium glutamate is the sodium salt of glutamic acid, one of the 20 amino acids found in proteins (see amino acids). In water it dissociates into sodium ions and glutamate ions — exactly the same glutamate found naturally in tomatoes, parmesan cheese, mushrooms and soy sauce. Glutamate is what gives these foods their savoury umami taste (see the chemistry of taste).

Your body can’t tell glutamate from MSG apart from glutamate from a tomato. Controlled, double-blind studies have not found consistent reactions to MSG at normal food levels. MSG actually contains about a third as much sodium by mass as table salt, so it can help reduce overall salt.

Myth 6: “Microwaving destroys nutrients” or “makes food radioactive”

What chemistry says: microwaves are a form of non-ionising electromagnetic radiation. They make water molecules — which are polar — rotate back and forth, and this motion becomes heat. They don’t have enough energy per photon to break chemical bonds or make anything radioactive.

All cooking can reduce some nutrients, especially water-soluble, heat-sensitive vitamins like vitamin C and folate, which leach into cooking water or break down with heat (see vitamin C chemistry). Microwaving often uses less water and shorter times than boiling, so it can actually preserve these vitamins better.

Myth 7: “Eggs are bad because they’re full of cholesterol”

What chemistry says: an egg yolk contains around 180–200 mg of cholesterol. For decades, people were advised to limit eggs. But for most people, dietary cholesterol has a relatively small effect on blood cholesterol, because the liver adjusts its own cholesterol production — it makes most of the body’s cholesterol itself (see cholesterol chemistry). Blood LDL cholesterol is influenced more by saturated fat, genetics and overall diet. Some people are more sensitive to dietary cholesterol, and advice for people with certain conditions differs, but many guidelines have relaxed strict limits on eggs.

Myth 8: “You need huge amounts of protein to build muscle”

What chemistry says: muscle is built from amino acids, and resistance training increases the body’s use of them. But the body can’t store excess amino acids as protein. Surplus amino acids have their nitrogen removed and converted to urea in the liver and excreted by the kidneys (see the kidneys as chemical filters); the carbon skeletons are burned for energy or stored as fat or glucose.

Research suggests benefits for muscle building level off at moderate intakes (often cited around 1.6 g per kg of body mass per day for people doing resistance training), spread across meals. Beyond that, extra protein doesn’t build extra muscle.

Myth 9: “Brown bread / brown sugar / brown eggs are always healthier”

What chemistry says: colour can mislead.

• Brown bread is healthier only if it’s actually wholegrain; some brown breads are white flour coloured with caramel or malt.
• Brown sugar is sucrose with a little molasses — nutritionally almost identical to white sugar.
• Brown eggs get their colour from a pigment called protoporphyrin deposited on the shell, and it depends on the hen’s breed. Inside, brown and white eggs are nutritionally the same.

Myth 10: “Vitamins from supplements are always as good as, or better than, food”

What chemistry says: some synthetic vitamins are chemically identical to those in food (ascorbic acid is ascorbic acid). But foods contain a whole mixture of compounds — fibre, minerals, dozens of vitamins and plant chemicals — and large supplement trials have often failed to reproduce the benefits of diets rich in fruit and vegetables (see antioxidants). Some supplements are clearly useful for specific people — for example, folic acid before and in early pregnancy, vitamin B₁₂ for vegans, and vitamin D in some climates (see vitamin D chemistry). But megadoses of fat-soluble vitamins (A, D, E, K) can accumulate and cause harm.

How to test a nutrition claim

1. Name the molecule. “Toxins”, “chemicals” and “nutrients” are vague; glutamate, sucrose and ascorbic acid are specific.
2. Ask about dose. A compound can be harmless or harmful depending on the amount.
3. Think about digestion. Most large molecules are broken down to small building blocks before absorption.
4. Look for controlled human studies, not just test-tube or animal experiments.
5. Beware single-food miracles. Diets matter more than individual “superfoods”.

Key takeaways

• A calorie is a unit of energy; foods differ in how the body handles them.
• Sea salt, pink salt and table salt are all mostly NaCl; iodised salt adds iodine.
• MSG provides the same glutamate found in tomatoes and cheese.
• Microwaves heat water molecules; they don’t make food radioactive and can preserve vitamins.
• The liver regulates cholesterol; excess protein is converted to urea and fuel.

For more everyday chemistry myths, see biochemistry myths.