"We are designed to go to sleep in between two and four - it's called the Circadian rhythm, and it's a hormonal peak in the afternoon that's telling us to go to sleep. If you're sleepy and tired, sugar and caffeine will get you through that. But the actual solution is to get your proper sleep and if you get eight hours at night and get some of it before midnight, it lessens the impact that the afternoon slump will have on you."

Fighting an after-dinner sugar craving

Often, even after a large dinner, thoughts turn to a sweet treat. Sarah's advice is to wait 15 minutes before breaking out the ice-cream. "You'll find that most of the time, after 15 minutes the desire of it is gone. That's a key thing to do in restaurants as well. When the meal is finished and they immediately hand you the dessert menu, don't even open it. Wait 10 or 15 minutes and once the signals have really arrived at your brain about what you've eaten, you'll realise you're full," she says.

"If after 15 minutes, you're still looking for something, dark chocolate is a nice thing to go for or one or two biscuits. The trick with the biscuits is that you put the two biscuits onto a plate and you take them to where you're going to eat them. You don't put the packet beside you." But she cautions that eating late at night generally has little to do with hunger. "You're eating because you're bored or usually because your body wants to go to sleep."

Snacking pre- and post-workout

"Experts differ, but for 30 minutes to two hours after a workout, having a snack does seem to improve the amount of muscle that you build and to refuel muscles for the next session," says Sarah. "But that can be coming home and having your dinner or it can be having a chicken sandwich on the way out the door."

Trainer and fitness expert Alan Williams suggests sticking to natural, whole snacks where possible. "I train more than most people and I don't eat shop-bought protein bars," he says. "While they're pretty high in protein, quite a few are high in sugar and they're very heavily processed - if you actually look at the back of the products and look what's gone into them, there's a list of ingredients as long as your arm and you probably don't know what half of them are."

Instead, he recommends snacks like nuts, and Greek or natural yoghurt with some chia seeds and berries stirred in. "If you've got a sweet tooth, rather than going for biscuits and chocolate, look at higher sugar fruits like a handful of grapes, but keep it in moderation and it will go a long way towards helping with cravings. I also say to people if they are having sugar cravings that half a banana is a good option as well."

Alan suggests having slow-release foods, such as porridge, or chicken with vegetables and rice two to three hours before a training session and then a simple carbohydrate like a banana or slices of apple dipped in nut butter 30 minutes before you train. Then, after a session, what you eat will depend on the time of day.

"It's something people overlook because they feel it's counterproductive to eat after you train but you've got to replenish lost stores and maintain muscle mass as well," says Alan. "A lot of people might be training after work so probably don't want to come home late at night and have a huge meal because it might affect your sleep. Try something like scrambled eggs with a slice of wholegrain bread so you're getting protein and a little bit of carbs or you could have one to two hard-boiled eggs, again with a slice of wholegrain bread. Two wholewheat crackers with a scraping of peanut butter and watermelon to replace lost electrolyte stores are good options.

"If you're training earlier in the day, you might want something heavier so something like sweet potato with chicken or turkey, or tuna with a slice of wholegrain bread."

Getting off the hormonal rollercoaster

Not all women have intense food cravings in the run-up to their period but an unstoppable urge to nibble can affect some.

According to Sarah Keogh, it's because of changes in insulin levels and your metabolism speeding up, too. "This is why you will look for more food and particularly sugary things the day or so before a period," she says. "Because your metabolism speeds up it doesn't have an impact on your weight. If it's one day I wouldn't worry about it, if it ends up being a week, you might want to put the brakes on.

"What does help are slow-release foods, like porridge, beans and lentils that tend to keep blood sugar levels a little more steady and that can help, but you are going to have a faster metabolism on those days so you are going to be hungrier."

The 'grandparents and treats' debate

Indulgent grannies and granddads can sometimes upset parents by giving children snacks that are at odds with the healthy eating patterns they are trying to instil at home. Sarah Keogh says that the issues are frequency and portion sizes. "I would ask how often is that happening. Is it once a week or once a month, in which case, I wouldn't worry about it," she says. "But I would just talk about amounts - it's one treat not five. Years ago you might bring a child one bar of chocolate, these days people turn up with a bag of stuff.

"A treat is not problem for a child and it's the wrong idea if you bring them up and give them nothing because then it becomes a much bigger deal for them later on, when they tend to over-eat. I would look at what the child eats all week and who else is giving them treats, and if it's just the grandparents on Friday, it's fine."