From the Journals

Varied diet not necessarily a high-quality one



A diverse diet is not necessarily a healthy one, according to an advisory issued by the American Heart Association that has instead emphasized the importance of a healthy eating pattern.

Published in the Aug. 9 online edition of Circulation, the science advisory was prompted by emerging evidence that greater dietary diversity may actually be associated with eating more poor quality foods and higher energy intake, especially among middle-aged adults.

Researchers conducted a literature search across 2000-2017 for studies of dietary diversity – defined as the number of different foods or food groups eaten over a given period of time – and dietary quality.

They found that observational evidence does not support the idea that a more diverse diet is associated with healthy weight or an optimal eating pattern. However, they also noted that many studies had significant limitations that contributed to high levels of inconsistency across all studies.

For example, one study in overweight and obese individuals found increasing dietary diversity was associated with a decrease in body mass index but with respect to intakes of only low–energy dense foods. Another study in Chinese adults saw an increase in diversity in the intake of snacks but not grains, vegetables, fruits, meats, or beverages, and this was associated with a 45% greater odds of being overweight, compared with individuals with a lower diversity of snack consumption.

Similarly, an observational study in 2,505 U.S. adults found individuals in the highest quintile of dietary diversity had a 120% greater gain in waist circumference, compared with those in the lowest quintile.

“Associations with dissimilarity scores are consistent with evidence from feeding studies showing that exposure to foods with different characteristics led to increased energy intake, which may partially explain gain in waist circumference over time,” wrote Marcia C. de Oliveira Otto, PhD, from the University of Texas Health Science Centre at Houston and coauthors.

The same was seen in short-term interventional studies, where most showed that having access to a wider variety of foods actually led to an increase in intake, compared with being served only a single food.

For example, one study showed adults offered a second course of sandwiches with different fillings to the first course actually ate 30% more than those served the same option for both courses.

Another study randomized overweight and obese adults to an unlimited number of snack options consumed less than once a day, or any amount of one favored snack option, with all snacks being within a daily caloric goal. This study found that, over the course of 8 weeks, participants offered a variety of snacks ate 25% more servings than those with the one snack type.

The authors suggested that variety amplifies sensory stimulation and decreases satiety.

“Although calorie restriction goals were achieved in both groups, a significant increase in sensory-specific satiety and monotony ratings over time was observed in participants assigned to the one-snack option but not in participants assigned to a variety of snacks,” they wrote.

The relationship between dietary diversity and dietary quality is also complex. Investigators for a cross-sectional study in China found less-than-optimal consumption of the nine food groups in the Chinese dietary guidelines – in particular, fruits, vegetables, fish, and dairy – in diets with higher diversity scores.

“Overall, limited evidence shows no benefit to diet quality or diet healthfulness associated with increased food count or with a more even distribution of energy across foods, whereas findings from one observational study suggest that greater dissimilarity in foods consumed may be inversely associated with a healthy eating pattern.”

In conclusion, the advisory committee said that it was more appropriate to promote a healthy eating pattern, emphasizing intake of plant foods, protein sources, low-fat dairy, vegetable oils, and nuts.

One author declared research funding from the Hass Avocado Board. No other relevant conflicts of interest were declared.

SOURCE: de Oliveira Otto MC et al. Circulation. 2018 Aug. 9. doi: 10.1161/CIR.0000000000000595.

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