An Ad Libitum Diet.

A low-fat, starch-based, vegan diet eaten ad libitum for 7 days results in significant favorable changes in commonly tested biomarkers that are used to predict future risks for cardiovascular disease and metabolic diseases. 

-Conclusions from the abstract of the research report entitled "Effects of 7 days on an ad libitum low-fat vegan diet: the McDougall Program cohort," reported in the Nutrition Journal 2014, 13:99.

Within the limits of a diet very similar to the one described in this report, I do not count calories nor otherwise limit what I eat.  I do not gain weight and I feel good. ("Ad libitum" means "at liberty" and is where we get the phraise "ad lib.")