No matter how many toning exercises you do, you'll never achieve the flat stomach you've always dreamed of if you don't eat the right foods.
But what about the foods to avoid if you want to get in shape?
Leading London nutritionist Rhiannon Lambert has shared with Femail Food&Drink the foods you should never eat if you want that flat stomach.
And while some, such as junk food and fizzy drinks, are a no brainer, others may surprise you - including 'healthy' lentils, onions and even apples.
"Foods high in fibre do have a tendency to make people produce large amounts of gas," says Rhiannon. This can lead to bloating in the stomach.
She continued: "Lentils are one of most fibre rich foods available typically over 15g per cup, cooked.
"But if you can't be without your lentils, it's worth noting that light colored lentils are generally lower in fibre than darker ones, and therefore, may cause less bloating.
"Other foods high in fibre include beans and artichokes."
"Dairy is an excellent source of protein and calcium with sources including milk, cheese, yoghurt and butter," advises Rhiannon.
"However, the US Library of Medicine says that with over 65 per cent of the world's population lacking the enzyme lactase, and therefore unable to break down lactose (the sugar found in milk), dairy can cause major digestive problems.
"If you're lactose intolerant, symptoms include bloating, gas, cramping and diarrhoea.
"Switching to fortified and unsweetened milk is always the best option, replacing dairy milk with unsweetened almond milk, for example."
Rhiannon says: "Although apples are great additions to a healthy diet given their high fibre, vitamin C and antioxidant rich contents, they are known to cause bloating and other digestive issues for some people.
"The combination of fructose and high fibre content means they ferment in your large intestine, which is likely to lead to gas and bloating.
"A cooked apple will be easier to digest than fresh ones. I like to bake apples for a tasty dessert with added cinnamon and a dollop of Greek yoghurt to stabalise blood sugar levels!"
"For those with celiac disease or gluten sensitivity, wheat causes major digestive problems," says Rhiannon. "This includes bloating, gas, diarrhea and stomach pain.
"However, this shouldn't be a problem for those who do not have a gluten sensitivity or are celiac and these items may also have added sugar, salt and chemicals so it is worth identifying the trigger before eliminating any food group or going gluten free."
Rhiannon says: "Junk food tends to be incredibly high in both fat and sugar and of course chemicals.
"Sugar empties from the stomach very quickly into your intestines, which alone causes cramping. That gassy and cramping experience often happens very quickly after consuming lots of high sugary foods.
"Conversely, the fats in junk food are some of the last things to leave the stomach, which can also cause discomfort and bloating.
"The extra additional chemicals found in these foods will also react poorly once inside the body and cause irritation, some people also note inflammation and markers on their skin after a large amount of junk food.
"The Journal Of Nutritional Biochemistry this year reported that artificial sweeteners are also linked to alterations in the guts bacteria and are linked to obesity."
Rhiannon says: "Salt binds to water in the body and helps maintain the balance of fluids throughout your system.
"By consuming processed foods, which are typically the biggest dietary source of sodium, or adding too much salt to food, your body may retain water."
"Even though they're usually eaten in small quantities, onions are one of the main dietary sources of fructans - soluble fibres that can cause bloating," says Rhiannon.
"Those that are sensitive to fructans will have discomfort especially when consuming raw onions.
"Cooking the onions may reduce these digestive effects. Alternatively, fresh herbs or spices can be used an alternative to onions."
"Carbonated drinks are another very common cause of bloating given they contain high amounts of carbon dioxide," Rhiannon says.
"When you drink something fizzy, you end up swallowing large amounts of this gas, some of which becomes trapped.
"This will cause some discomfort to your digestive system, which can result in bloating and even cramping.
"Beer is one of the worst culprits of bloating as it's made from sources of fermentable carbohydrates like barley and wheat. Containing gas (carbon dioxide) and fermentable carbs, beer has two well-known causes of bloating.
"Hydration is the cornerstone of good health, and with the average Briton drinking less than one glass of water a day, drinking water rather than fizzy drinks will do you some good."
TIPS TO REDUCE BLOATING
Rhiannon has three tips for how to beat the bloat, which she has shared below:
1. DON'T EAT TOO MUCH
Being overly full can feel like being bloated, but the issue is that you simply ate too much. If you're eating big meals and feel uncomfortable afterwards, smaller portions are the way forward.
Also, chewing your food better can have a significant effect. It will reduce the amount of air you swallow with the food.
Don't forget that the type of meal can also effect this, a high carbohydrate focused meal could result in what I also call the 'food baby' as you retain water to each carbohydrate molecule, your heavy feeling is often simply water weight.
2. EAT PROBIOTICS
Gas produced by the bacteria in the intestine is a major contributor to bloating. With so many different types of bacteria living in our intestine, it's clear that the number and type of bacteria greatly impacts our gas production.
A number of studies suggest probiotic supplements can help reduce both gas production, as well as bloating, especially in people with digestive problems.
3. CHECK FOR FOOD ALLERGIES
Rule out any food allergies and intolerances. Consuming foods that you are intolerant to can cause excess gas production, bloating and other similar symptoms.
Some common foods and ingredients that you may be intolerant to include: lactose, fructose, eggs, wheat and gluten.
Avoiding some of these can help you establish any allergies but if you strongly suspect that you have a food allergy or intolerance, it is best to see your GP or a registered nutritionist.