" Good Morning America" teamed up with Reader's Digest on a special series, " 13 Things Experts Won't Tell You."

This month, Reader's Digest unveils the secrets weight loss professionals won't tell you, like how to maximize your workouts, what may be holding you back from losing weight and how to get the most bang for your buck.

1. Do not arrive at a training session in the following states: a. on an empty stomach, b. coming off a cold/stomach bug, or c. on four hours' sleep. It wastes your time and a personal trainer's when your body isn't fueled, hydrated and ready to work.

2. If you find your workouts are getting a little stale, a trainer is a great way to put some pep in your push-ups. If you can't afford one, get some friends together for a small group session. They cost less per person - and working out with friends is proven to improve your commitment and overall weight loss.

3. To kick start your metabolism, opt for intervals. In a recent study, women who did 20 minutes of cycling sprints lost three times as much fat as those who cycled slowly and steadily for 40 minutes.

4. When you hit the point where you think you can't go on, imagine you have a trainer right next to you, cheering for you. Studies show that actively encouraging yourself improves outcomes.

5. You can do OK at the drive thru. There are now some reasonable options if you look for them. Stay away from anything with the word "crispy," steer clear of all mayo-heavy sauces (use mustard instead) and stick to no-fat dressing.

6. Nibble on the move. If you are shopping and fading from hunger, avoid settling in at the food court and, instead, nibble your way through a shopping marathon. Pick up a snack, such as a hot pretzel, a small bag of roasted nuts from a kiosk or even a chicken taco and nibble on the move. Portable meals can still weigh you down, so check calorie counts on your mobile phone before you go.

7. Douse your afternoon slump or hunger pangs with water. The energy drop that hits in afternoon is likely a combination of perfectly natural factors - the results of a light lunch, mild dehydration, a momentarily lack of iron or a crash off that coffee you had at the late-morning meeting. Before wandering to the cafeteria or fridge, start your recovery with a tall glass of water, which boosts your blood flow and, as a side benefit, makes you feel full.

8. It's hard to win against a cookie. While food is not addictive the way cocaine or alcohol is, there are some uncanny similarities. When subjects at Monell Chemical Senses Center in Philadelphia were shown the names of foods they liked, the parts of the brain that got excited were the same parts activated in drug addicts.

9. Your bedroom, not the kitchen might be making you fat. Sleep deprivation upsets our hormone balance, triggering both a decrease in the hormone leptin (which helps you feel full) and an increase of the hormone ghrelin (which triggers hunger). As a result, we think we're hungry even though we aren't - and so we eat. Sleep may be the cheapest and easiest obesity treatment there is.

10. Your weight really is genetic. When scientists first discovered a gene in certain chubby mice, they called it simply the fatso gene. Turns out, people with two copies of the gene were 40 percent more likely to have diabetes and 60 percent more likely to be obese than those without it. Those with only one copy of the gene weighed more too. But your "destiny" is no excuse.

11. Ear infections can taint your taste buds. In one study of more than 6,000 people, researchers found that people over age 35 who had suffered several ear infections had almost double the chance of being obese. Why? These infections can damage a taste nerve running through the middle ear. When researchers found the at former ear-infection patients were a little more likely to love sweets and fatty foods, they theorized that the damaged nerve might cause them to have a higher threshold for sensing sweetness and fattiness.

12. Fat might be your mom's fault. A growing body of science suggests that sugary and fatty foods consumed even before you're born can mess with your weight.

13. At dinner, make yourself useful serving people and cleaning up. It gets you away from your plate, but still makes you a vital part of the meal.

*Web Extra Tips: What Your Personal Trainer Won't Tell You*

• If you concentrate on the exercise you are doing with the same intensity as talking about the latest gossip about your life, you would find it easier.

• Trainers know you are eating more than you tell them.

• It takes more than writing a check or showing up for training sessions to make you fit and healthy. It's what you do before and after you meet with your trainer, including choices with food, alcohol and workouts, and a commitment to a new lifestyle.

• Ask you trainer what she or he does to keep educated in the field. An educated trainer will get better results and provide variety to keep you engaged and motivated in your workouts.

• When you are late, it is a waste of your money, a waste of my time and disrespectful.

• Trainers see through your stall tactics. "I think I need to fill my water bottle." "Let me get a dry towel real quick." "Oh, I need to go to the bathroom again." Nice try. But you're paying for the session, so make every minute count.

• There is a difference between pain and burn, and you need to be honest with your trainer about which you're feeling. If you push so hard that you injure yourself, you both lose.

• Whatever the text or email says, it can wait until you're done with your workout. And no, you cannot text and put forth 100 percent effort at the same time.

• The trainer does not have time to get sick. Cancel your session if you're carrying germs.

• Gear matters. Don't expect to get maximum performance and results by working out in the ratty gym shoes and shorts you dug out of that old box of college dorm clothes. Invest in a good pair of sneakers. Your feet and joints will thank you, and so will your trainer.

• Remember that a 30-minute session at max effort is better - and cheaper - than 60 minutes of dawdling and half-effort.

• Stop whining and push through those last few reps.