It’s no secret that Americans are fatter today than ever before, and not just those unlucky people who are genetically inclined to gain weight or have been overweight all their lives. Many who were lean as young adults have put on lots of unhealthy pounds as they pass into middle age and beyond.

It’s also no secret that the long-recommended advice to eat less and exercise more has done little to curb the inexorable rise in weight. No one likes to feel deprived or leave the table hungry, and the notion that one generally must eat less to control body weight really doesn’t cut it for the typical American.

So the newest findings on what specific foods people should eat less often — and more importantly, more often — to keep from gaining pounds as they age should be of great interest to tens of millions of Americans.

The new research, by five nutrition and public health experts at Harvard University, is by far the most detailed long-term analysis of the factors that influence weight gain, involving 120,877 well-educated men and women who were healthy and not obese at the start of the study. In addition to diet, it has important things to say about exercise, sleep, television watching, smoking and alcohol intake.