1.Eat all the time. Have you ever seen a fat hummingbird? Chances are, the answer is “no” unless it has some kind of metabolic disorder. The vast majority of hummingbirds are three things: slim, constantly moving, and constantly eating. We can certainly learn from these tiny, frenetic animals. Eating (small snacks) 5-6 times a day instead of gorging on three big meals actually puts the body into hyper-drive. Metabolism revs up and calories get burned. The opposite: long periods of fasting (as in "3 square meals") makes the body into an energy miser. It goes into starvation/conservation mode and begins to store fat. That’s the body’s natural answer to the question “hmm, I wonder when my next meal will be?”
TIP: Eat small meals (e.g. an apple and some string cheese) every 3 hours until about 7PM.

2.Turn on and tune up your mitochondria. At the cellular level, energy comes from power-packed mitochondria. They’re mostly located in muscle tissue and their main role is providing energy for lifting a dumbbell and/or that triple decker whopper you’re eating. As we get older, we begin to lose mitochondria and, thus, the ability to make food into energy. The unfortunate result is that the body stores up that unused food as fat. TIP: Exercise to increase mitochondria. You’ll have more energy and less fat.

3.Don’t stress out, workout. There are about 100 ways to gain weight and stressing out is one of the top ten. Don't stress out about it, though, because turning this around is simple. Instead of stressing out do some physical activity. You'll gain muscle which helps you to burn calories. This is especially important because as we age, muscle begins to shrink (a condition known as sarcopenia). So if you’re over 40 exercise is doubly important. While you're combatting the muscle wasting, the exercise also helps you to feel better and decrease stress hormones that can lead to weight gain. TIP: Workout to look and feel better

In summary, follow the way of the hummingbird, nature’s marvelous athlete. Eat (nutritious food) constantly and don’t stop moving.