A study of more than 25,000 healthy middle-aged American females with an average age of 55 found that following a diet rich in fish, legumes, vegetables, nuts, and whole grains was linked with a 23 percent lower risk of dying by the end of the 25-year study. 

Every woman was quizzed on their adherence to the diet annually, and thos who stuck closely to it over that 25-year period enjoyed a 16 percent lowered risk of death from all causes.  

The Mediterranean diet, which has been crowned the best diet for seven years in a row, has been shown to reduce inflammation in the body, improve the body's regulation in insulin, and manage weight, all of which protect against heart disease, dementia, and diabetes.   

The diet is common in Greece, Italy, and Spain, countries that border the Mediterranean Sea. 

The latest study from Harvard University is among the largest, with 25,315 women involved and perhaps the longest-running, with the women being followed for more than two decades.

At the start of the study, women filled out health questionnaires about their dietary habits, their health, their height and weight to calculate BMI. 

They also had their blood pressure assessed.

Participants filled out health questionnaires every six months during the first year and annually thereafter. 

Researchers assigned scores for adherence to the diet on a scale from zero to nine, with a higher score indicating that the woman stuck to the diet closely.

The scoring was based on the intake of nine dietary components, including a high intake of vegetables (except potatoes), fruits, nuts, whole grains, fish, and monosaturated fats.

If a woman ate less red and processed meats, she got points. If their alcohol consumption fell between five to 15 grams per day, they got an additional point. 

Then, the participants were broken into three categories based on their scores, with low adherence scores ranging from zero to three, intermediate adherence scores being a four or five, and high adherence scores falling between six and nine.