The world of nutrition is unfortunately subject to much quackery and this, combined with ever-increasing numbers of people looking for magic nutrition solutions to improve their health or help them lose weight, means many mythological food beliefs persist. Of course there are some beliefs that do have a scientific grounding. In this week's column I will attempt to sort the wheat from the chaff.

Eating carbohydrates in the evening will make you fat

An upward swing on the scales occurs when you fail to use up as many calories as you consume each day. Calories eaten in the form of carbohydrates (such as pasta, rice or bread) at night, behave no differently to those consumed earlier in the day and will only pile on the pounds if you have already eaten your quota of calories for that day. Of course, it makes more sense to eat more food at the time of day when you need more fuel, so for many a heavier meal at lunch and a lighter meal in the evening makes sense. The lighter evening meal should certainly still include carbohydrates as this is what your body uses for energy, and if you are about to have at least 8 hours without eating - you need something to keep your bodily functions ticking over.

Eating sugar causes diabetes

Type II Diabetes is caused by a number of things and being overweight is one of the most significant risk factors, worse still if this weight is on your tummy. However, sugar itself cannot cause diabetes. It can contribute to weight gain if eaten in excess, just like fatty foods, alcoholic drinks or indeed any food eaten in large amounts. Once you have been diagnosed with diabetes, it then becomes very important that you don't eat too much sugar in one go (although you can still eat a little) because your body is unable to control the rate at which this sugar goes into your blood stream and this is dangerous for your health.

Carbohydrate and protein foods cannot be digested properly at the same time

Somehow this myth continues to pollute the minds of vulnerable dieters despite a complete lack of scientific grounding. The concept of food-combining dates back to the late 1800s when Dr William Hay came up with the theory that the enzymes which digest protein and carbohydrate are respectively acidic and alkaline so these neutralize each other if present at the same time. This neutralization would apparently cause food to ferment and rot in the gut. Thankfully this has no scientific basis whatsoever. Firstly the pancreas produces both carbohydrate and protein digesting enzymes at the same time no matter what food is eaten. Secondly all food in the stomach is treated with acid and so becomes acidic. It then travels through to the small intestine where it is all treated with alkali. Thirdly many highly nutritious foods such as rice, lentils and beans naturally contain large amounts of both protein and carbohydrate and these are digested very efficiently by the body.

Carrots make you see in the dark

Well, sort of - carrots are a great source of beta carotene which is converted to vitamin A in the body and is essential for good vision. One of the symptoms of vitamin A deficiency is a condition called night blindness, when the eyes have difficulty adjusting to dim light. But chomping through a sack of carrots will not result in a superhuman ability to see clearly in the dark, especially if you are not vitamin A deficient in the first place. Beta carotene can also be obtained from many fruit and vegetables apart from carrots especially those that are orange and dark green in color such as pumpkin, persimmon, papaya, broccoli and pak choi.

Please contact me if you have any more nutrition myths you are curious about.

This nutrition-related column is written by Nina Lenton, a qualified dietitian living in Beijing and working at Bayley and Jackson Medical Center. Contact her at nina.lenton@ikang.com

(China Daily 12/14/2007 page14)