Keeping track of how much you eat by writing it down each day, rather than what you eat, is key for weight loss, a new U.S. study suggests.

The No. 1 piece of advice would be to keep a food journal to document every morsel that passes your lips and thereby help monitor daily calorie intake, concluded researchers at the Fred Hutchinson Cancer Research Center in Seattle, Wash.

“It is difficult to make changes to your diet when you are not paying close attention to what you are eating.” said lead investigator Anne McTiernan.

Participants in the study were given a printed booklet to record their food and beverage consumption, but a food journal doesn't have to be fancy.

"Any notebook or pad of paper that is easily carried or an online program that can be accessed any time through a smart phone or tablet should work fine," McTiernan said.

Other specific behaviours that support weight loss include not skipping meals and avoiding eating in restaurants – especially at lunch.

The findings were published online Friday in the Journal of the Academy of Nutrition and Dietetics

The study focus was on how self-monitoring and other diet-related behaviors, as well as meal patterns, effect weight change in overweight and obese postmenopausal women.

"When it comes to weight loss, evidence from randomized, controlled trials comparing different diets finds that restricting total calories is more important than diet composition such as low-fat versus low-carbohydrate,” McTiernan said.

The study involved 123 overweight-to-obese, sedentary, Seattle-area women, aged 50 to 75, who were randomly assigned to two groups: one group tried to lose weight based on diet alone, while the second group relied on exercise plus diet.

In the year-long study, participants filled out a series of questionnaires to assess dietary intake, weight-control strategies, self-monitoring behaviors and meal patterns. They also filled out a 120-item food-frequency questionnaire to assess dietary change from the beginning to the end of the study.

At the end of the study, participants in both groups lost an average of 10 per cent of their starting weight, which was the goal of the intervention.

Among the study’s findings:

- Women who kept food journals lost about six pounds more than those who did not.

- Women who skipped meals lost almost eight fewer pounds than women who did not

- Women who ate out for lunch at least weekly lost on average five fewer pounds than those who ate out less frequently (eating out often at all meal times was associated with less weight loss, but the strongest association was observed with lunch).

Eating at regular intervals and avoid skipping meals, is another effective weight loss strategy, the study found.

"The mechanism is not completely clear, but we think that skipping meals or fasting might cause you to respond more favorably to high-calorie foods and therefore take in more calories overall," McTiernan said.

"We also think skipping meals might cluster together with other behaviors. For instance, the lack of time and effort spent on planning and preparing meals may lead a person to skip meals and/or eat out more."

Meanwhile, eating out frequently in restaurants may make it difficult to make healthy dietary choices because it usually means less control over ingredients and cooking methods as well as larger portion sizes, the study concluded.