Even though entrepreneurs are ultimately measured by their ability to increase earnings and profits (since without profits you don't have a business), great entrepreneurs are almost always great with people.

No one does anything worthwhile alone. Leaders are only great when they build great teams--which means making every person on those teams better.

That's why great leaders know how to praise their employees. They provide useful, timely feedback. They know, in general terms, what they should and should not say.

Of course, if you're going to do all that, you need to be upbeat. You need to be switched-on so you can motivate and inspire your employees.

Which is really hard to do when you're feeling down and depressed.

Which is why soda--especially diet soda--may not be your friend.

According to a 10-year study of over 260,000 people, those who drank over four cans of soda per day were 30 percent more likely to be depressed than those who didn't drink any soda.

Those who drank coffee, on the other hand, were 10 percent less likely to be depressed than those who drank no coffee.

Artificial sweeteners seem to be the culprit. As the researchers write, 

"Unlike sugar-sweetened drinks, diet drinks often use artificial sweeteners such as aspartame and saccharin for the sweet taste and are calorie-free.

"Our further analysis found that adding these artificial sweeteners to coffee or tea, but not adding sugar or honey, was associated with higher risk of depression.

"Various effects of artificial sweeteners, including neurological effects, have been suspected. For example, aspartame may modulate brain neurotransmitters such as dopamine and serotonin.

"Our research suggests that cutting out or down on sweetened diet drinks or replacing them with unsweetened coffee may naturally help lower your depression risk."

Which is a bummer for Diet Mtn Dew drinkers like me. Unlike some, I'm not anti-caffeine. I try not to drink too much--it's hard to love the jittery feeling that results--but I do drink a few diet sodas throughout the day.

And I don't think they affect my mood...but then again, I don't know that. It's hard to know if something is affecting you if you always do that thing--artificially creating a steady state over a long period of time automatically creates a sense of "normal."

Since I like trying unusual experiments, for the next two months I'm going to stop drinking diet soda. (And anything containing artificial sweeteners, since aspartame, saccharin, etc., appear to be the depression culprits.)

To replace the morning "pick me up" I get from the caffeine in a diet soda, I'll go back to a tried-and-true mood-boosting technique: 20 minutes of moderate cardio first thing in the morning. 

Research shows that 20 minutes of low- to moderate intensity aerobic exercise three times a week makes people feel less fatigued and more energized. (The time of day doesn't matter; work out a little, feel a little better.) Even five minutes of moderate exercise can create a mood-enhancement effect.

But more to the point, other research shows that aerobic training of "moderate intensity," with an average heart rate of around 112 beats a minute--working, sure, but not cranking--improves mood for up to 12 hours after exercise.

Try it: Work out when you first get up and you'll naturally feel more energetic. And be in a better mood.

Without diet soda, and the negative side effects that might result.

Check back a couple months from now and I'll tell you how it went for me.