There is a sure-fire way to lose weight; if you eat two cheeseburgers at McDonald's, eat one. 

You don't need to read any books, slow cook, give up gluten, give up dairy, fats, carbs or booze; those can all help in the short term, because you are shocking your body and it mobilizes to deal with that, but over the long term just eat less. All diets work if you stick to them.

A new study has again affirmed what every weight loss study done by people not selling you something has found; weight loss differences between popular diets are minimal and likely of little importance to those wanting to lose weight. Staying on the diet is the most important thing - behavioral support and exercise enhance the weight loss but the eating less matters most.

You don't need a celebrity to show you how to eat fewer slices of pizza.

"We wanted to be the first to compare, in an evidence-based fashion, all existing randomized trials of branded diets to determine their effectiveness with regard to weight loss," says Bradley Johnston, an assistant professor of clinical epidemiology of the Michael G. DeGroote School of Medicine at McMaster University and lead authors of the paper in the Journal of the American Medical Association (JAMA).

The scholars did a meta-analysis of 48 randomized clinical trials of branded diets, including more than 7,200 overweight and obese adults with a median age of 46 years. The research team assessed weight loss at six and 12 months.  Branded diets included in the studies were Atkins, Weight Watchers, Zone, Jenny Craig, LEARN, Nutrisystem, Ornish, Volumetrics, Rosemary Conley, Slimming World and South Beach, among others. 

The study was needed, says Geoff Ball, associate professor in the Faculty of Medicine&Dentistry at the University of Alberta. "Given the popularity of these diets around the world, there has been a real lack of research to examine their relative benefits. But overall, the differences between the different diets regarding their impact on weight loss were relatively small."

Johnston notes that the findings are particular to people who followed branded diets over the short-term, and who adhered to the diet. Future research may focus on long-term effectiveness, as well as on outcomes related to overall health.

At six month follow-up, people on low-carbohydrate diets lost 19 more pounds than those who were not on a diet, while those on low-fat diets lost 17 more pounds than those on no diet. After 12 months about two to three pounds of that difference was gone, and there was no difference between low-carbohydrate and low-fat diets.

Behavioral support in a diet made a difference at six months, enhancing weight loss by about 7 pounds, while exercise was significant at 12 months, improving weight loss by about four and half pounds.