Most people realize that the mind and body are connected into a feedback loop. "A healthy mind in a healthy body" is why psychologists and physicians alike recommend sensible eating and regular exercise.
Neuroscientists, however, recommend a different approach. Because they know that body-centric lifestyle changes (like diet and exercise) are difficult to maintain, they recommend starting with the mind. And they've identified the one thought that, when regularly focused upon, is most likely to propel your mind and body into an upward spiral.
That thought? Gratitude.
Yes, that sounds all crunchy granola, but there's actually extensive research into the positive mental and physical effect of that specific thought and emotion, according to a fascinating article published by the Wharton Health Care Management Alumni Association. Here are some highlights:

1. Gratitude makes you more likely to exercise.

According to the Journal of Personality and Social Psychology, people who keep gratitude journals "reported fewer health complaints, more time exercising, and fewer symptoms of physical illness." 

2. Gratitude reduces your stress level.

According to a study published by National Center for Biotechnology Information "cultivating appreciation and other positive emotions showed lower levels of stress hormones [specifically] a 23 percent reduction in cortisol and 100 percent increase in DHEA/DHEAS levels."

3. Gratitude improves the quality of your sleep.

According to a study conducted at the University of Manchester and published in the Journal of Psychosomatic Research, regularly focusing on gratitude and thankfulness "improved quality of sleep and [resulted in] longer sleep hours."

4. Gratitude increases your emotional well-being.

According to studies published in the Journal of Research in Personality,  gratitude leads to lower depression and higher levels of social support while making you less likely to consider suicide.

5. Gratitude makes your heart stronger and healthier.

According to research conducted at Massachusetts General Hospital, the presence of gratitude in a patient "may independently predict superior cardiovascular health." Other studies show that gratitude increases the physical activity and therefore the speed of recovery for heart patients while reducing their inflammatory biomarkers.

6. Gratitude makes you a more effective leader.

According to a Wharton study, grateful leaders "motivated employees to become more productive [because] when employees feel valued, they have high job satisfaction, engage in productive relationships, are motivated to do their best, and work toward achieving the company's goals."
In some of the studies, participants kept a gratitude journal in which they'd list at the end of the day all the reasons they felt grateful. That's a good technique, but you can feel gratitude all day by simply asking yourself, "What can I feel grateful for right now, right here?" Your brain will come up with an answer.