Stay slim forever

Wondering why you can't eat as much chocolate as you did in your 20s without putting on the pounds? Finding it more difficult to lose weight as you get older? Well, it turns out your skirt length, skincare regime and social life aren't the only things that change over time - so does how your body loses and gains weight.

Whatever your age - 20s, 30s, 40+ - make sure your eating habits aren't to blame for inch gain.

Our guide to what to eat and why should help you master your metabolism and help you stay in control of your changing body.

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In your 20s

Why you're gaining weight:

First the good news: your metabolic rate is now higher than ever, so your body will be burning off cake-loads of calories. However, your fun social life could be counteracting all that. This is supported by research showing that women in their 20s eat 25% more fast food than they did in their teens. And with such a crammed diary, you may be struggling to find time to exercise. Yet another reason why your skinny jeans might be pinching.

How to halt it:

In order to lose weight quickly and easily, a diet full of nutrients is essential for fun-loving 20-somethings.

These include wholegrains and foods high in vitamins B and C, as well as omega-3 fats to help boost your levels of serotonin, the feel-good chemical that helps reduce stress and anxiety. Also aim for plenty of vitamin B6-rich foods, such as chicken, bananas and nuts, so you'll have plenty of energy left for partying.

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In your 30s

Why you're gaining weight:

Unless you're eating less or exercising more, the chances are you've noticed it's harder to keep the weight off. In fact, according to research, 40% of 30-something women gain weight during this decade.

The reason? Your metabolism has started to slow down. Not only this, but you may have also noticed your shape has changed and you've gained weight around your bottom, hips and thighs. Whether you're trying to conceive or not, this is because your body is trying to store more fat to fuelpregnancy and breastfeeding.

But that's not all: trying to juggle your home, partner, career, friends and family can be stressful, and research shows this can further slow down your metabolic rate and increase the likelihood of a build-up of abdominal fat.

[See also: 7 tinned foods no slimmer should be without]

How to halt it:

To crank up your metabolism, eat regular small meals and snacks containing protein, such as low-fat yogurt or nuts.

Your diet should also be nutrient-rich to stave off tiredness, and low GI to keep energy levels up throughout the day. And for pregnancy planning, you should include folate-rich foods. And fret not; the right carbs, eaten in the right quantities, won't make you gain weight.

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From your 40s, 50s and 60s

Why you're gaining weight:

You're not imagining it - your metabolism has slowed right down - by about 100 calories a day, in fact. This isn't just due to ageing, but because after 40 you start to lose about 1-2% of calorie-burning muscle mass each year.

It's also when the perimenopause - the run-up to the menopause - tends to strike, causing oestrogen