I came across an interesting study in PLOS Medicine: https://journals.plos.org/plosmedicine/ on diet and longevity: Estimating the impact of food choices on life expectancy: A modeling study. Based on data from the Global Burden of Disease study (2019), published in The Lancet, the researchers modeled the effect of three diets on life expectancy (LE) using multivariate regression. The diets compared were the extant typical Western diet (TW), an optimized diet (OD) where longevity was maximized, and a feasibility approach diet (FA). This last eating pattern represents a mid-point between TW and FA, which is considered more feasible for European and American consumers.

Average Daily Consumption of Various Foods for Each Diet
Food Western Diet
Feasibility Approach
Optimal Diet Comments on Optimal Diet Portions
Whole grains (fresh weight) 1.75 4.8 7.9 oz
(2.6 oz dry weight)
~ 7 servings: 2 thin slices of rye bread, 1 small bowl of whole-grain cereal, some whole
grain rice
Vegetables 8.8 11.5 14.1 ~ 5 servings: 1 big tomato, 1 sweet pepper, mixed salad leaves, half an avocado, small
bowl of vegetable soup
Fruits 7 10.6 14.1 ~ 5 servings: banana, orange, kiwi, a handful of berries
Nuts 0 0.45 0.89 1 handful of nuts
Legume 0 3.5 7.1 1 big cup of soaked lentil/beans/peas
Fish 1.8 4.4 7.1 1 big slice of fish
Eggs 1.8 1.3 0.9 1/2 egg
Milk/dairy 10.6 8.8 7.1 1 cup of yogurt
Refined grains 5.3 3.5 1.8 e.g., refined grains in bread if mixed with whole/refined wheat
Red meat 3.5 1.8 0  
Processed meat 1.8 0.9 0  
White meat 2.6 2.2 1.8  
Sugar-sweetened beverage 17.6 8.8 0  
Added plant oils 0.9 0.9 0.9  


The health gains from FA and OD arise mostly from reductions in cardiovascular disease, cancer, and diabetes.

The impact of diet on LE is affected by the age at which the diet is adopted. Below is a table of the age-specific gains in LE at different ages for the diets compared to the TE. The LE values are for persons living in the U.S.


 Age-proportional LE Gains in the U.S. Population
 Age Male FA Gain Female FA Gain Male OD Gain Female OD Gain
 20  7.3  6.2  13.0  10,7
 40  6.5  5.7  11.7  10
 60  4.8  4.5  8.8  8
 80  1.9  2.0  3.4  3.4


I find a few things interesting about this study. Note that it essentially describes the Mediterranean Diet as its optimal diet. This is unremarkable to me. There are no recommended amounts of red or processed meats. Two items that contribute substantially to healthier diets are nearly absent from the average daily consumption of the TW: legumes and nuts. The amount of added oil is minimal; I presume this means salad dressing, too.

I acknowledge that correlation does not mean causation. However, the data sets used are worldwide and across all age populations. The dose response is in direct proportion for all age groups. I strongly suspect causation is indicated.