One of the interesting aspects of studying nutrition is finding causation. Most studies showing the benefits of fruit and vegetable consumption are associational. In an associational study you notice a pattern among a group of people. You then say, “People who live to be 80 consume 7 servings of fruits and vegetables a day. So you should probably consume 7 servings of vegetables a day.” Indeed, people who eat a lot of fruit tend to be leaner, smarter, and healthier in old age.
Yet a skeptic could rightly not that perhaps something else was at play, arguing, “People who eat vegetables are healthy in other respects. How can we know that it’s vegetables rather than something else that is responsible for the favorable health results?
A recent study (via Science Daily) shows a causal relationship between dietary intake of fruits and vegetables and mood:
Department of Psychology researchers Dr Tamlin Conner and Bonnie White, and Dr Caroline Horwath from Otago’s Department of Human Nutrition, investigated the relationship between day-to-day emotions and food consumption.
On each of the 21 days participants logged into their diary each evening and rated how they felt using nine positive and nine negative adjectives. They were also asked five questions about what they had eaten that day. Specifically, participants were asked to report the number of servings eaten of fruit (excluding fruit juice and dried fruit), vegetables (excluding juices), and several categories of unhealthy foods like biscuits/cookies, potato crisps, and cakes/muffins.
In other words, the researchers asked, “What did you eat last night and how did you feel today?”
The results showed a strong day-to-day relationship between more positive mood and higher fruit and vegetable consumption, but not other foods.
“On days when people ate more fruits and vegetables, they reported feeling calmer, happier and more energetic than they normally did,” says Dr Conner.
That’s not surprising to me. Processed food is literally loaded with neurotoxins. Everyone who has begun juicing has reported improved mood.
The implication is a welcome one. If you want to feel better tomorrow, make a juice today:
To understand which comes first – feeling positive or eating healthier foods – Dr Conner and her team ran additional analyses and found that eating fruits and vegetables predicted improvements in positive mood the next day, suggesting that healthy foods may improve mood. These findings held regardless of the BMI of individuals.
How many servings of fruits and vegetables should you eat to be happy?
“After further analysis we demonstrated that young people would need to consume approximately seven to eight total servings of fruits and vegetables per day to notice a meaningful positive change. One serving of fruit or vegetables is approximately the size that could fit in your palm, or half a cup. My co-author Bonnie White suggests that this can be done by making half your plate at each meal vegetables and snacking on whole fruit like apples,” says Dr Conner.
That recommendation is consistent with our earlier post. See, “How many servings of fruits and vegetables do I need?” A 16-ounce glass of juice meets the researcher’s recommendations.
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