On the face of it, dieting and exercise are equally good at shedding the pounds - as long as the number of calories consumed is the same as the number of calories burned. After all, weight loss occurs whenever you burn more calories than you take in.
So, is dieting or exercising the best way to go - or should you always do both? We take a look at both sides of the argument...
Diet vs Exercise
"If you can exercise enough to burn more calories and would rather do that than cut calories, then exercise is the way to go," says David L. Katz, M.D., associate professor of health at Yale University School of Medicine.
"If, however, you're more willing to trim your portions than go out running, dieting will work better," he adds.
"It's nearly impossible to exercise enough to control weight without attention to diet," says Katz.
In contrast, studies show that the majority of people who have lost weight and kept it off for five years or more combine diet and exercise.
And while you can't beat aerobic exercise for burning calories, weight training is just as beneficial for weight loss.
A study published in the Journal of Applied Physiology found that, though weight training doesn't burn as many calories as cardio, it significantly increases the average daily metabolic rate – helping you shed the pounds even faster.
"Many truly obese people don't eat much but don't move much, either (hence their weight stays the same).
Some are eating at starvation levels but sit in a chair all day. If these people would start moving, they would begin to lose weight," says sports medical expert Stephen Rice.
American researchers compared African American women in Chicago with women in rural Nigeria. On average, the Chicago women weighed 184 pounds and the Nigerian women weighed 127 pounds.
To their surprise, researchers found no significant difference in activity levels between the two groups. "Decreased physical activity may not be the primary driver of the obesity epidemic," concluded nutritionist Amy Luke.
Those who exercise maintained their strength and muscle mass and increased aerobic capacity – unlike those who dieted, who lost muscle mass, strength and aerobic capacity.
"If push comes to shove and somebody wants to know if they should diet or exercise to lose weight, I would suggest exercise, provided they are willing to put in the extra time and effort and not offset the gains they make by eating more," said lead researcher Edward Weiss, Ph.D.
Keeping active strengthens bones and muscles, improves mental health and mood, lowers blood pressure, improves cholesterol levels and reduces the risk of cardiovascular disease, diabetes and cancer.
Keeping active has also been shown to help you get a good night's sleep and improve sexual functioning.
Dr Rachel Thompson, deputy head of science for WCRF said: "There is now very strong evidence that being physically active is important for cancer prevention. Even relatively modest increases in activity levels could prevent thousands of cancer cases in the UK every year.
"By taking up walking as a hobby or even walking to the shops instead of taking the bus or car, people can make a real difference to their health."
Recent studies suggest that a third of all cancers cases are related to diet.
The advice is to eat plenty of fruit and vegetables (especially green leafy ones), make sure you're getting enough fibre and limit the amount of processed and red meat you consume.
So what's our verdict? A combination of diet AND exercise is best if you want to stay healthy and lose weight and keep it off.