We all know that to have a healthy, balanced diet we should try to eat more fruit and veg, cut back on fatty, sugary, salty and processed foods, and exercise regularly.

But what about those happy eaters who think nothing of having a couple of takeaways a week, love a pizza with extra cheese and toppings, munch through crisps at lunchtime, never go to the gym, and still look trim and fit?

[Read more: Diet fizzy drinks: What you need to know]

It’s one of life’s little mysteries that a Channel 4 programme hopes to unravel: The Truth About Slim People. By carrying out different tests to see if people have ‘magic metabolisms,’ monitoring what time of day they eat and how often they snack between meals, and most tellingly, whether they spend hours planning meals, dietitians and health experts hope to reveal how to stay slim without having to fast.

In the meantime, here are seven tips to help anyone struggling with their weight…

1. Walk more and take the stairs

If you’re desk bound, try to go out of your way to take the stairs, walk up the steps to the top of the bus, walk to the tube station, park at the far end of the car park and walk at a fast pace.

2. Don’t snack between meals

Munching on biscuits at elevenses is just as naughty as having crisps and chocolates in the car journey home, or on the sofa watching TV. Studies show you’re better off to eat more at mealtimes, rather than graze at your desk.

[Read more: 3 delicious juices to keep you healthy in winter] 

3. If you eat a lot one day, eat less the next

Everyone looks forward to a delicious blow out meal, especially at the weekend. But what you don’t want to do is overeat the next day. Try to eat a bit less, but not in a planned way, more in a sensible, ‘I really enjoyed that massive dinner last night, so will be careful today,’ way.

4. A little bit of everything does you good

If you love cheese, eat cheese, but in a smaller amount. Have a sweet tooth? Great, reach for dark chocolate and just have a couple of squares, rather than the whole bar. Adore chips? Of course you do, but have them at set mealtimes, take it easy on the salt and limit consumption.

[Read more: 12 classic breakfasts from around the world]

5. Eat at the table with a knife and fork

Sounds mad, but eating with a knife and fork and not your fingers makes more of an occasion of the meal and is a very good habit to get into. Even if you’re eating a delicious pastry or a sandwich, try eating it slowly with cutlery and you’ll feel fuller for longer.

6. Cut back on alcohol

According to the experts, excessive wine consumption not only piles on the calories (an average glass of wine contains as many as a slice of cake) but alcohol in your system also affects how fats and sugars are digested.

7. Get a good night’s sleep

Try to go to bed by 11pm most nights to get a good night’s sleep. Studies have shown that chronic poor sleepers, those sleeping less than six hours a night on a regular basis, tend to develop a variety of conditions including weight gain.