Some food reputations are older than the science. Spinach is not an iron powerhouse, carrots won't give you night vision, orange juice doesn't stop colds, honey is still sugar and pink salt is still salt. None of these foods is bad. They just don't do what many of us were told.
1. Is spinach really one of the best sources of iron?
Not really. Half a cup of boiled spinach has about 3 mg of iron, according to the US National Institutes of Health (NIH). That's a fair amount, similar to half a cup of cooked white beans. But it is non-haem iron, the plant form, which the body absorbs less well than the haem iron in meat and fish. Spinach also contains oxalates and polyphenols that hold on to iron and reduce absorption further.
The NIH estimates that people absorb roughly 14 to 18% of the iron from mixed diets that include meat and fish, and 5 to 12% from vegetarian diets. That's why vegetarians are advised to aim for more iron overall.
The famous story that spinach's reputation came from a misplaced decimal point is itself probably a myth. A criminologist, Mike Sutton, traced the story in 2010 and found no evidence for the decimal error. The story is still widely repeated, but no original source for the error has been found.
What helps: spinach is still a good vegetable, rich in folate and vitamin K. If you rely on plants for iron, pair them with vitamin C. The EU allows the claim that "vitamin C increases iron absorption", so a squeeze of lemon on your spinach or peppers in your lentil salad is a sensible habit.
2. Do carrots help you see in the dark?
Only if you are short of vitamin A. Carrots are rich in beta-carotene, which the body turns into vitamin A, and vitamin A is essential for the eyes. According to the NIH, the first sign of vitamin A deficiency is night blindness, difficulty seeing in low light.
But once you have enough vitamin A, extra carrots won't sharpen your vision. Eat a lot of them for a long time and the most likely result is carotenodermia, a harmless yellow-orange tint to the skin that fades when you eat fewer.
The idea is usually traced back to the Second World War, when Britain is said to have credited its pilots' night-time success to carrots rather than reveal its new radar. Whether or not every detail is true, the message stuck long after the war.
3. Does orange juice (or vitamin C) keep colds away?
For most people, no. A Cochrane review (Hemilä and Chalker, 2013) looked at 29 trial comparisons with more than 11,000 participants. Taking vitamin C regularly did not reduce how often ordinary people caught a cold.
There were two smaller findings worth knowing:
- Regular vitamin C shortened colds a little, by about 8% in adults and 14% in children on average.
- In people under heavy physical stress, such as marathon runners and soldiers in subarctic conditions, regular vitamin C roughly halved the risk of colds. These were small groups, though.
Taking vitamin C only after a cold starts showed no consistent benefit in the trials.
Vitamin C does have an authorised EU claim: it contributes to the normal function of the immune system. That's not the same as preventing colds. And if your vitamin C comes from orange juice, remember that WHO counts fruit juice as free sugars, like added sugar. A whole orange gives you the vitamin C with the fibre and without the free sugars.
4. Is honey healthier than sugar?
Not in any way that matters much. Honey has tiny amounts of other compounds, but nutritionally it is mostly sugars, the same glucose and fructose found in table sugar. The World Health Organization (WHO) counts honey, syrups and fruit juices as free sugars, in the same group as the sugar you add to coffee.
WHO strongly recommends keeping free sugars below 10% of daily energy, and suggests below 5%, about 25 g or 6 teaspoons a day, for extra benefit. A spoonful of honey counts towards that limit just as much as a spoonful of sugar. The same goes for brown sugar, date syrup and agave.
Honey is fine to enjoy for its taste. Just don't treat it as a free pass.
5. Is pink Himalayan salt better than ordinary salt?
The minerals are real but the amounts are tiny. A 2020 Australian study (Fayet-Moore and colleagues) tested 31 samples of pink salt. It found that you would need to eat more than 30 g a day, about six teaspoons, before the extra minerals made a meaningful difference. That much salt would be very harmful. One sample also had lead above the national safety limit.
WHO recommends that adults eat less than 5 g of salt a day, about a teaspoon, and the global average is roughly double that. Whatever its colour, salt is mostly sodium chloride, and the real health question is how much you eat. One more point: the white salt in the Australian study was iodised, which is a useful source of iodine. Pink salt usually isn't, so check the label if you switch.
So what should we take from this?
No single food is a "champion". The foods above are all fine as part of a varied diet, and spinach, carrots and oranges are very good foods. The problems start when a reputation makes us rely on one food for something it can't deliver, or eat more of something, such as honey or salt, because it sounds healthier. If you are worried about iron, vitamin A or any other nutrient, a blood test through your doctor tells you far more than any food myth.
FAQ
Is spinach still worth eating?
Yes. It provides folate, vitamin K and fibre, and some iron. Eating it with a source of vitamin C, such as lemon juice or peppers, helps your body absorb more of that iron.
Should I take vitamin C when I feel a cold coming?
In the Cochrane review, starting vitamin C after symptoms appeared showed no consistent benefit. Regular intake shortened colds slightly but did not prevent them in most people.
Is sea salt better than table salt?
Like pink salt, sea salt is mostly sodium chloride and the same limit of less than 5 g a day applies. Iodised table salt has the advantage of providing iodine.
Sources: NIH Office of Dietary Supplements, Iron fact sheet for health professionals, NIH Office of Dietary Supplements, Vitamin A and carotenoids fact sheet, Sutton M, Spinach, iron and Popeye: ironic lessons from biochemistry and history on the importance of healthy eating, healthy scepticism and adequate citation, Internet Journal of Criminology 2010, Hemilä H, Chalker E, Vitamin C for preventing and treating the common cold, Cochrane Database of Systematic Reviews 2013, CD000980, WHO, Guideline: Sugars intake for adults and children (2015), WHO, Sodium reduction fact sheet, Fayet-Moore F et al., An analysis of the mineral composition of pink salt available in Australia, Foods 2020, 9(10):1490, Regulation (EU) 432/2012 (list of permitted health claims).
