The worst is when they think some food is good for you and some is bad, and that if you don't follow some very narrow, arbitrary rules that bear no relation to scientific fact you will die a gruesome early death.
Like the insistence that calories make you fat, cholesterol will give you heart disease and YOU MUST EAT BEANS.
Well, that's bollocks.
Someone who eats nothing but kiwi fruit has a diet just as bad as that of someone who eats nothing but chicken nuggets. One kiwi fruit has about the same number of calories as half a bag of Maltesers, whereas chicken nuggets are an excellent source of protein. A slice of chicken breast has more calories than a Mars bar, but no-one would argue it's bad for you.
Orange juice has SEVEN TIMES as many calories as a cup of coffee, a strawberry yoghurt has nearly as many grams of fat as a hamburger, and an avocado has the same amount of fat as a quarter pounder with cheese. Alcohol is ram-packed with calories, but I've lost count of the number of times someone's told me they're on a diet while sipping a large glass of wine.
There is more vitamin C in a bag of chips than in an orange. Jaffa cakes contain less fat than a bowl of cornflakes. There is more vitamin A in liver than in an apple. Cocoa beans are packed with fat, but if you eat chocolate with a high cocoa content it helps protect your heart.
There's nothing wrong with calories - without them you couldn't move. There's nothing wrong with cholesterol - it is a vital constituent of every single cell in your body. There is nothing wrong with fat - we are evolved to digest, store and burn it. It's having too much of those things and not doing anything to work them off which causes trouble, and that alone.
What we are not evolved to deal with is man-made rubbish. So it's the trans-fats in processed food and takeaways which stay lodged in our bodies, undigested, and get packed around our cells because our livers cannot get rid of them quickly. It's preservatives, emulsifiers and chemicals which do not exist in nature, the wrong kind of fat, which causes us problems.
If you put a tub of butter outside on a summer day, it will be surrounded by insects pretty quickly. It's a natural source of energy and animals will lap it up. If you put a tub of margarine next to it the insects will leave it untouched, because margarine was invented by man as a nasty paste to fatten up turkeys and even ants disdain it.
Take this example. A doctor put two trays of processed food on her surgery counter in 2010 and 2011 respectively. Neither has decreased in size, grown mould, or decayed in any way. What makes you think that your liver and kidneys want to take it on?
A study of half a million people over eight years found those who ate lots of fruit and vegetables had exactly the same incidence of breast, prostate, bowel, lung and other cancers as those who didn't. Cancer is caused by genetic and environmental factors, as well as chemicals in the diet. You can eat all the fruit you like but if you smoke or live downwind of a paint factory it's won't help much.
There are 13 vitamins and according to biochemists the three that come in fruit - A, C, K1 - can be absorbed by the human body only if they are accompanied by fat molecules. So strawberries will do you more good if you have cream with them. All the other vitamins, by the way, have better sources in other food groups, not least of which is red meat.
Too much sugar, calories and fat is obviously bad for you. But a little bit of everything, whether it's strawberries, scones, steak, kiwi fruit or Victoria sponge, is absolutely fine, in fact it's the healthiest kind of diet to have. And better still if it's as natural as possible and the ingredients on the label don't include a long-named chemical compound which is a total mystery to you.
Butter doesn't kill people - stupidity does. And if you needed any proof you need only to look at the picture below. One woman is 52 and eats butter, red meat and cream. The other is 53 and eats mainly mung beans and man-made tofu. I know one has a spinal condition and isn't wearing make-up, but personally I think they look like there's 40 years between them.
You will also notice that only one of them is smiling.
