A toned body and flat stomach is everyone's dream. But having a sluggish metabolism plays havoc with our efforts to lose weight. Metabolism is the amount of energy or calories your body burns to maintain its vital functions and speeding this up is the key to weight loss. To speed up the metabolic process, try incorporating some of these foods into your meals. Not only do they boost metabolism, they also help to stave off cravings, reduce water retention and keep you feeling fuller for longer. Water: Simple, and yet so effective. Drink plenty of fresh water. To keep metabolism burning at full speed, drink the recommended two litres a day (about eight glasses). Almonds: Despite the fact that they are relatively high in calories, almonds themselves do not contribute to belly fat. Swap out your usual mid-morning snack for a handful and see if it makes a difference. Pistachios: If you're looking to trim down your belly, then pistachios, together with almonds, are one of the best nuts you can snack on. They are lower in calories and fat than most other nuts, while remaining high in protein, fibre and other essential vitamins and minerals. Apple cider vinegar: It acts as a digestive tonic, helping to slay off harmful bacteria in the intestines, flush out toxins and relieve water retention around the stomach. Try adding some to vegetables during cooking or as a dressing over salad. Asparagus: Each spear is packed full of vitamins A, B-complex, C and E, and contains high levels of skin-clearing zinc and potassium, which assists in the removal of excess fluids from the body. Asparagus has long been used to treat inflammations, such as arthritis and rheumatism. Tomatoes: Delicious, full of antioxidants and they also help you to lose weight. Tomatoes are definitely among the fat-fighting foods. They have been found to reduce inflammation and water retention in the body. Chilli: It boosts your metabolism, and helps you to burn fat faster. A single chilli pepper also contains a full day's supply of beta-carotene, which is great for maintaining healthy skin, hair and nails, and twice your recommended daily allowance of vitamin C. Bananas: Contrary to what some people believe, bananas contribute to weight loss. Eating a banana provides your body with skin-healing zinc and filling fibre. It also helps to relieve water retention thanks to the high levels of potassium it contains. Watercress: It includes vitamins B1, B2, B6, C and E, as well as minerals manganese, carotene and potassium. This makes watercress a powerful cleansing agent, improving digestion and nourishing the skin, while its diuretic properties help to flush out toxins and excess fluids. Watercress is also a fabulous source of iodine, which helps to boost metabolism and achieve a flat stomach. Cucumber:It is a natural diuretic, which means consuming it eases water retention and bloating in the body. Make a slimming watercress, tomatoes, mint and cucumber salad for a powerful tummy-flattening lunch. Ginger: It's used as a digestive aid, because it possesses anti-inflammatory, anti-nausea and antioxidant properties. It also contains an enzyme called zingibain, which helps digest proteins. Artichoke: It's rich in fibre, thus helping to speed the digestive process up and relieve bloating in the abdomen, while containing relatively few calories. Pineapple: It boasts a digestive enzyme that helps to ease bloating, settle your stomach and even relieve heartburn.