Unsaturated fats, especially polyunsaturated, help reduce age-related weight gain.
Dietary fat content and change in the composition of the fats you eat and their effect of weight loss and management are very controversial topics. There are weight loss diets that focus on eating amounts of fat to induce ketosis and lower your carbohydrate intake. Many tout the benefits fo a higher fat diet for all kinds of illnesses. The fact remains that the relationship between dietary fat intake and body weight is controversial and you are unlikely to find two dieters or experts with the same beliefs.
Few studies have examined long-term changes in types of dietary fat and weight change that are associated with these changes. One study published in September of 2018 in Journal of Nutrition looked at this very question. This study specifically looked at the associations between intake of different types of fat and long-term weight change in US women and men. In the study, the association between changes in consumption of varying types of fat and weight change was examined every 4 years and the results were adjusted for age, baseline body mass index, and change in percentage energy from protein, intake of cereal fiber, fruits, and vegetables, alcohol use, and other lifestyle differences in 3 prospective US cohorts that included over 120,000 men and women. The subjects were free of diabetes, cardiovascular disease, cancer, or obesity over a 20- to 24-year follow-up. Dietary intakes and body weight were assessed with questionnaires. The researchers found that compared with equivalent changes in carbohydrate intake, a 5% increase in energy from saturated fatty acid with 0.61 kg greater weight gain per 4-year period. Conversely, a 5% increase in energy from polyunsaturated fatty acids was associated with less weight gain (−0.55 kg).