Do you wing it without a plan, tell yourself you will 'eat healthily and exercise more' and let that be the end of it?
Or do you spend hours poring over forums, books, magazines and websites looking for the best diet plan that will work for you?
The NHS website has published a list of the top diets people follow, with pros, cons and a verdict given by the British Dietetic Association.
Read on for reviews of 12 diets and if you've ever tried to follow them, we'd love to hear your thoughts on how easy they are to stick to and how well they worked for you.
Fill in the form at the bottom of the article to get in touch.
What is it?
The Atkins diet is a low-carb, high-protein weight loss programme.
How does it work?
You start with a low-carb diet designed for rapid weight loss. This lasts at least two weeks, depending on your weight loss goal. During this phase, you’re on a protein, fat and very low-carb diet, including meat, seafood, eggs, cheese, some veg, butter and oils.
During the next three phases, the weight loss is likely to be more gradual, and regular exercise is encouraged. More carbs, fruit and veg are introduced to your diet, with the aim of working out what your ideal carb intake is to maintain a healthy weight for life.
Phase one is designed to help you lose up to 15lb in two weeks, reducing to 2lb to 3lb during phase two.
What does the British Dietetic Association say?
"Rapid weight loss can be motivating, but it is unsustainable. The Atkins diet isn’t nutritionally balanced. By limiting fruit and veg, it contradicts all the healthy eating advice that we have tried so hard to pass on to people.
"The meal choices are limited, so there’s a risk many people will get bored quickly and drop out or take a "pick and mix" approach."
The diet consists of foods that can be hunted and fished – such as meat and seafood – and foods that can be gathered – such as eggs, nuts, seeds, fruits, vegetables, herbs and spices.
It’s a regime based on the supposed eating habits of our hunter-gatherer ancestors during the paleolithic era, before the development of agriculture around 10, 000 years ago.
That means cereal grains including wheat, dairy, refined sugar, potatoes and salt – as well as anything processed – are strictly off the menu.
There is no official "paleo diet" but it is generally seen as a low-carb, high-protein diet, with some variations on carbohydrate and meat intake.
What's the verdict?
"Most versions of the paleo diet exclude key food groups, raising the potential for nutritional deficiencies unless careful substitutions are made, and dietary supplements may be necessary.
"The diet has some positive aspects, so an adapted version that doesn't ban any food groups – such as wholegrains, dairy and legumes – would be a better choice.
"The diet lacks variety, so there’s a risk you’ll get bored quickly and give up. If you want to copy your paleolithic ancestors, you’re better off mimicking their activity levels, rather than their alleged diet."
The 5:2 diet is based on a principle known as intermittent fasting (IF) – where you eat normally for five days a week and fast on the other two days
What does the BDA think?
"This is a simple way to reduce calorie intake. There are lots of versions of this diet, with some less safe than others. If you choose to follow it, choose an evidence-based plan based on healthy, balanced eating and written by a dietitian, such as the "2-Day Diet".
"It’s vital for your health to avoid nutritional deficiencies, dehydration and overeating on non-fast days. Never attempt to delay or skip meals if you are pregnant, have had, or are prone to, eating disorders or diabetes."
It is essentially a calorie-controlled diet, where you get a personal daily ProPoints allowance, which you can use how you like. There’s no limit on the amount of fruit and most veg you can eat.
You also get a weekly ProPoints safety net in case you go over your allowance, and an individual exercise plan
The weekly meetings and confidential weigh-ins provide support and extra motivation to encourage long-term behaviour change. The plan is designed to help you lose up to 2lb a week.
The BDA verdict:
"The ProPoints plan is generally well balanced and can be a foundation for long-term changes in dietary habits.
"The support group approach can help keep people motivated and educate them about healthy eating.
"It’s vital that you make the connection between the points system and calories if you want to avoid putting the weight back on once you leave the programme."
The Slim-Fast diet is a low-calorie meal replacement plan for people with a BMI of 25 and over.
It uses Slim-Fast’s range of products. The plan recommends three snacks a day from an extensive list, including crisps and chocolate, two meal replacement shakes or bars and one regular meal, taken from a list of recipes on the Slim-Fast website.
You can stay on the diet for as long as you want, depending on your weight loss goal. Once reached, you’re advised to have one meal replacement shake a day, up to two low-fat snacks and two healthy meals.
What do the experts think?
"If you don’t like the taste of the meal replacement products, you won't stay with the plan.
"The Slim-Fast plan can be useful to kickstart your weight loss regime, but it’s important that you make full use of the online support to learn about the principles of healthy eating and how to manage everyday food and drink."
South Beach diet
The South Beach Diet is a low-GI diet originally developed for heart patients in the US.
There's no calorie counting and no limits on portions. You're encouraged to eat three meals and two snacks a day and follow an exercise plan.
People who have more than 10lb to lose start with phase one. This is a two-week quick weight loss regime where you eat lean protein, including meat, fish and poultry, as well as some low-GI vegetables and unsaturated fats.
Low-GI carbs are re-introduced during phases two and three, which encourage gradual and sustainable weight loss.
The BDA verdict
"The first two weeks are the most difficult to get through. We’re concerned that this diet promises such a large weight loss, up to 13lb, in the first two weeks. This, however, won't be all fat.
"Some of the weight loss will include water and carbs – both of which will be replaced when you begin eating more normally.
"Once you get past the initial phase, the diet follows the basic principles of healthy eating and should provide the nutrients you need to stay healthy."