There is no research evidence that shows women need more sleep than men. You would be forgiven for thinking otherwise, with headlines such as Metro’s “Women actually need more sleep than men so let’s all go back to bed”. At Loughborough University’s sleep research centre, the reputed source of this revelation, they don’t know where this myth comes from. Its director, Kevin Morgan, even has a problem with what “more sleep” actually means.

Surveys show women report having less, and poorer quality, sleep than men. Morgan says women take longer to get to sleep and wake up for longer in the night. He thinks a combination of hormonal and societal factors influence women’s sleep. Progesterone and oestrogen influence mood, which can affect the quality of sleep. Then there is pregnancy, getting up for children and the menopause (causing shorter, lighter and more fragmented slumber).

Studies show that women multitask more than men, which has led to suggestions that the more active female mind needs more sleep. There is also research showing that the downsides of not having enough sleep affect women more than men – that blood tests of inflammatory markers of disease are higher in women. This theoretically increases their risk of heart disease. But since women probably don’t (marginally) get as much sleep as men, it is hard to say what “more” means. Is it amount or quality? The jury, if not the media reporting, really is out.

Can I lose weight if I stop eating by 8pm?

If only losing weight were as easy as that. There is no good evidence that humans metabolise calories any differently in the evening than at other times, so this “hard stop” at 8pm works only if it helps you eat fewer calories. Our normal circadian rhythms (body clocks) seem to encourage eating in the evening – few people are hungriest in the morning. A study using an app to monitor food intake found more than half of the subjects ate during a 15-hour period each day. Less than a quarter of calories were eaten before noon and more than 35% after 6pm. When overweight people who ate for more than 14 hours a day were restricted to eating for 10 to 11 hours over a period of 16 weeks, they lost weight and slept better.

This builds on work at the Salk Institute in California showing mice that were allowed to eat only for eight hours at night when they were most active, and forced to fast for 16 hours a day, were slim despite being fed a high-fat diet. They were as lean as those in a control group on regular food, and proved the fittest on an exercise wheel.

The study spawned a slew of media articles suggesting an ice-cream eaten at midday was somehow metabolised better than one enjoyed during House Of Cards. But mice are not humans. Research shows that eating at night is associated with weight gain because munching is done on high-fat snacks rather than celery sticks. The longer people stay up, the more likely they are to take in more calories – up to two pounds a month, according to a study. Anything that restricts calorie intake, such as closing the kitchen at eight, will help lose weight, but only if the calories eaten beforehand and the energy expended are balanced out.

If I stop exercising, will my muscles turn to fat?

It is no more possible for muscles to turn to fat than for bones to turn to cheese. There are actually three different types of muscle cells; smooth ones that line the walls of organs such as the stomach; cardiac ones, found only in the heart; and skeletal muscle cells, which are the only ones under voluntary control. These resemble stripy-looking fibres under a microscope and get bigger when you exercise. You don’t develop more muscle cells when you exercise – the ones you have just enlarge. Stop getting fit and your muscle cells shrink.

If you aren’t using those muscles, there’s no point in the body spending energy (calories) in feeding them. Muscle cells eat up an extra two-thirds of the calories that fat cells do, so the muscle bulk gets reduced and the ratio of fat to muscle increases. This is why anyone who has bulked up goes from six-pack to flab if they stop going to the gym.

Muscle cells cannot morph into fat cells, which are fairly simple structures. Fat accumulates under the skin and when you gain weight the number and size of cells increases. If you stop exercising but don’t reduce your calorie intake, your fat cells will multiply and grow. But what they can’t do is become muscle cells, and vice versa.