At your annual health checkup with your primary care doctor, the discussion turns to your diet. You gained 10 pounds this year. You explain that you are juggling a busy work schedule and try to prepare a balanced, home-cooked diet. However, you also note that you often resort to take-out or fast food. You ask your PCP whether such an inconsistent diet can have long-term health and survival consequences.
The 2015 Dietary Guidelines for Americans recommend healthy dietary patterns without focusing on single nutrients or foods. However, the effect of changes in diet quality and patterns over time on mortality is uncertain. A study by Sotos-Prieto et al. published this week in NEJM sheds some light on this question. The investigators analyzed the association between changes in diet quality over 12 years (1986-1998) and risk of death (from 1998 through 2010) among 47,994 women in the Nurses’ Health Study and 25,745 men in the Health Professionals’ Follow-up Study.
Based on food frequency questionnaires and using three diet-quality scores (the Alternate Health Eating Index-2010 score, the Alternate Mediterranean Diet score, and the Dietary Approaches to Stop Hypertension [DASH] diet score DASH score), diet quality and mortality were consistently associated. Adherence to any of the three dietary patterns (as assessed by a 20% increase in diet scores) was associated with a mortality reduction of 8% to 17%, while worsening diet quality over 12 years was associated with an increased mortality risk of 6% to 12%. The change in mortality risk was more pronounced after long-term (16 years) than shorter-term (8 years) follow-up and for overall and cardiovascular mortality. Null or weaker associations were observed between improvements in diet quality and cancer mortality.
In both cohorts, participants with greater increases in diet quality were younger, more physically active, had lower baseline diet scores, and consumed less alcohol and sodium and more whole grains, vegetables, and n-3 fatty acids. These findings are consistent with those from other studies.
Strengths of the study include the two large prospective cohorts with high rates of follow-up, repeated assessments of diet and lifestyle, and use of multiple diet quality scores. However, since most participants were white health professionals and dietary patterns were extracted from self-reported questionnaires, the generalizability of the results to other populations is uncertain.
You and your primary care physician conclude that the consistent associations between improved diet quality and lower risk of death underscore that modest improvements over time in diet quality might meaningfully influence your mortality risk. You leave your appointment feeling motivated to maintain a more consistent healthy dietary pattern.
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Bhavna Seth is a Resident at Boston Medical Center.