Weight loss pills and supplements that work

... and the pros and cons to consider before you take them

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There are all kinds of foods and supplements that promise to help you lose weight - but most of them don't actually work. If you're looking for help to slim down (alongside a calorie-restricted diet and exercise), here are four weight loss foods and supplements that have been shown to work.

See also: Six reasons you can't lose weight

See also: Ten tricks to downsize your appetite

1. Glucomannan
You might have seen konjac noodles sold as a weight loss food in health food shops. Konjac, also known as glucomannan, is a type of fibre sourced naturally from the roots of the elephant yam.

So what's special about it? Once consumed, glucomannan absorbs water and swells to become gel-like in your stomach, making you feel fuller and so reducing your appetite.

There are several brands of konjac noodles, rice and pasta available. While the texture isn't quite the same as the real thing, they don't taste of anything – so eaten with your normal vegetables/meat and a sauce you shouldn't notice much difference. A bowl of noodles contains less than 20 calories and no carbs. Five packs (200g each) of Slim Water Eat Noodles cost £8.95.

You can also take glucomannan in liquid form – mix up the sachet of powder with water and stir (it will start to thicken) and consume 30 minutes before your meal. Skinny Sprinkles, for example, costs £24.95 for 21 servings from Amazon.

Several studies have found that people who take glucomannan, combined with a healthy diet, lose more weight than those who just stick to a healthy eating plan. Some people, but not everyone, find that glucomannan causes bloating, flatulence and soft stools.

2. Orlistat (Alli)
Orlistat is a weight loss drug, sold over-the-counter as Alli, and available on prescription as Xenical.

Taken in tablet form, it works by blocking the enzyme that breaks down fats in your diet. Instead of being broken down and absorbed, this undigested fat is expelled from the body when you use the bathroom. Because Orlistat only works on fat, and doesn't stop the body absorbing calories from sugar and other non-fat foods, so need to restrict your total intake of calories in order to lose weight.

Several studies have proven its effectiveness. Overweight people who took the drug lost 6 pounds more than those who took a dummy pill while following a low-fat, healthy diet.

However, the drug has some very unpleasant side effects – and is not suitable for many people because of this. As well as frequent bowel movements (which may be hard to control) and loose, oily stools, it can result in tummy discomfort and flatulence. If you're taking Orlistat it's vital to eat a low-fat diet if you don't want to experience its side effects!

3. Caffeine
Caffeine is found naturally in coffee, green tea and dark chocolate – and thanks to its metabolism boosting properties, is added to many popular weight loss supplements.

Short-term studies have shown that caffeine can boost metabolism by 3-11%, and increase fat burning by more than 25%. However, it's not without side effects – as anyone who has had the 'jitters' from drinking too much coffee will know. Large amounts of caffeine can result in tummy upsets, along with anxiety, irritability and problems sleeping.

If you plan to use caffeine as a metabolism booster you may as well skip the supplements and just enjoy a few cups of coffee or green tea, both of which contain antioxidants and have other health benefits.

4. Green tea extract
Green tea extract contains an antioxidant called EGCG, which has been shown to boost the activity of norepinephrine, a hormone that helps the body burn fat. While the effects are relatively slight, studies have shown that it can help with weight loss and burn fat, especially belly fat.

Unlike many fat burning supplements, green tea extract is generally well tolerated. As it contains some caffeine, in may cause problems for people who are caffeine sensitive. Matcha Tea Extract (120 weight loss capsules) costs £9.97.

It's worth remembering that any weight loss supplement only has a slight effect - and that restricting your calories and exercising more is by far the best way to lose weight.