Susan Edmunds has a few practical suggestions - and warnings - to achieve weight loss.

Protein bars, sports drinks, meal-replacement shakes ... if you have spent any time at a gym lately you'll be familiar with these. But do they really work? And are they a necessary part of your fitness regime?

If you are trying to lose weight, success depends on a very simple equation: the number of calories you consume must be fewer than the number you burn. But if you give a bit of thought to the make-up of your diet, it can make the weight-loss process more satisfying and enjoyable.

What you should be aiming for is a diet that contains the right amount of energy (calories) and provides all the nutrients the body needs. All food is made up of carbohydrates, protein and fat. You need elements of all three.

There's a lot of buzz about protein because of its role in building muscle. Jacquie Dale of Real Nutrition says protein bars and supplements do have their place. "If your goal is to tone up and drop some winter flab, then protein shakes and bars can be a good fit in your diet."

But, she says, more important is to know exactly how many calories a day you should be aiming to eat. "A kilo of fat contains about 8000 calories. So to lose fat, 90 per cent of your result will come from what you put in your mouth. It's the same scenario with muscle gain. There's no point working hard at the gym without a good diet."

She says having a protein bar in your bag might make you less likely to snack on junk food or skip a meal.

During long workouts, sports drinks can be useful. Choose varieties that have up to 10 per cent carbohydrates, as they will enter the bloodstream in time to deliver energy to muscles. Drinks with more carbohydrates can cause cramps.

When it comes to carbohydrates, opt for those low on the glycaemic index such as porridge and all-bran cereals. They take longer to be broken down by the body and so give a more sustained energy boost.

When you eat is important, as well as what. Eat five or six smaller meals over the course of the day rather than three big ones. Avoid high-fibre foods just before your workout.

Don't skip breakfast but opt for something that combines carbohydrates and protein: cereal with milk or fresh fruit and yoghurt. For lunch, top up your protein again with a salad and chicken sandwich. For dinner, opt for a meal including lean protein like grilled fish, teamed with rice and a salad.

Eat slowly - you're less likely to eat too much as your body will have time to register you're satisfied.

"Find out how much you should be eating and when. It's never as hard as you imagine," Jacquie says.