I wonder if this is true.
Pretty much. There are ongoing long term studies of groups like Seventh Day Adventists and Okinawans whose diets are like this. Much lower rates of cardiovascular disease and certain cancers. The Med diet, the DASH diet, WFPB whole food plant based are often prescribed for diabetics or heart or kidney patients. The last time my rare kidney disease flared up part of the treatment included a consultation with a dietitian. Her recommendations were basically this kind of diet, which I’d already been doing for several years. It’s not a cure but it increases your chances of being healthy.