Nutrition science is hampered by the inability to randomize people into various treatment approaches. Thus, when we see that some individuals who, for example, eat more fish, we are unable to conclude that the difference in their outcome is related to their diet or related to other factors that we cannot control. It could be that individuals who eat fish may exercise more, have more money, smoke less or have less stress.
That being said, we can find associations that may be meaningful. Into this mix, another study (M Sotos-Prieto et al. NEJM 2017; 377: 143-53) find that a better diet quality is associated with lower total and cause-specific mortality.
This study analyzed two large cohorts:
- The Nurses’ Health Study -a prospective study with 121,700 RNs –enrollment initiated in 1976
- The Health Professionals Follow-up Study with 51,529 health professionals enrollment initiated in 1986
Diet quality was evaluated with three scoring systems:
- The Alternate Healthy Eating Index with 11 food components
- The Alternate Mediterranean Diet Score with 9 food components
- The Dietary Approaches to Stop Hypertension (DASH) with 8 food components
- “A 20-percentile increase in diet-quality scores was associated with an 8 to 17% reduction in mortality”
- “Worsening diet quality over 12 years was associated with an increase in mortality of 6 to 12%.”
- “Taken together, our findings provide support for the recommendations of the 2015 Dietary Guidelines Advisory Committee that it is not necessary to conform to a single diet plan to achieve healthy eating patterns.”
- “Common food groups in each score that contributed most to improvements were whole grains, vegetables, fruits, and fish or n-3 fatty acids.”
Like most nutrition studies, this one has limitations. Strengths of this particular study include the prospective design, large sample sizes, repeated assessments of diet/lifestyle, multiple diet assessments, and high rates of followup.
My take: There is no doubt that diet quality is associated with improved longevity. Better diets are highly likely to be the reason why many people live longer.