While out to dinner with my friend N. the other night, she eyed me as I read the menu.  “I’m not ordering until you do,” she said, leaning back while crossing her arms and leaving her menu untouched. Something was strange about that; N. being a person who always tore into a menu with enthusiasm and gusto. But this time was different. Borrowing a line from When Harry Met Sally, Nora told the waitress, “I’ll have what she’s having.”

“So…what’s up with that?” I asked. N. had always ordered what she wanted, not concerned with details like salt content or calorie counts. And she never had to be concerned: she’s the friend I wrote about who still fit into the jeans she wore all those years ago, back in high school

N. stared at me, her face serious. “I have never been this heavy in my life,” she said. She took a gulp of water. “Except when I was pregnant.  I just hate getting older.”

“Didn’t you tell me you recently joined a gym?” I remembered her enthusiasm, telling me about how she had been going four to five days each week.  “Are you still going?”

“Of course!” she answered. “I work out so much. I get home and I’m absolutely famished.”

“What do you eat after you exercise?”

“I usually stop for a bagel and cream cheese and when I get home I pour myself a big glass of orange juice. That’s healthy…isn’t it?”

It’s a common misconception that we can eat whatever we want since we’ll burn it off exercising. The painful truth is this: You don’t burn as many calories as you think from exercise. In other words, just because you are sweating and working hard, it doesn’t give you free license to eat whatever you want. (click here for a chart of different activities and an estimated total of what your body burns). Simply put, eat more than you burn off, and the weight will follow.

Another part of the puzzle: As you age, metabolism gradually becomes more sluggish with each decade after age 20. You don’t suddenly wake up and poof- you’re 10 pounds heavier. It happens slowly, over time. Compared to age 25, at 35 you burn about 100 fewer calories a day. At 45, that number becomes 200 fewer…you get the picture.

You might be tempted now to throw in the towel at this news-not so fast!  There are ways to fight this slowdown:

Change your fitness routine. It’s easy to get complacent, bored, comfortable with the second-treadmill-from–the-right-with-the-best-view in the gym. But when you get used to a certain routine, it’s likely that you’ll forget to work hard. You’ll go through the motions, just to get it over with; familiarity at the gym breeds less challenge. Don’t forget to have fun and let your inner energy emerge: push yourself and try other fitness options like spin, Zumba, kickboxing or whatever else is new and exciting. If you walk, intersperse it with short bouts of jogging; if you like to bike, alternate easy pedaling with more resistance.

Add some peppers to your diet. Capsaicin, the chemical compound in chile peppers that gives them their heat, can also rev up your metabolism. Although studies show the effects are fleeting, it can add up over a long period of time, especially if you love eating spicy foods. You can add red pepper flakes to so many foods: pastas, stews, chilis, pizza…breakfast cereal (?).

Pick up some weights. People whose bodies have more muscle have more efficient metabolisms; that’s because each pound of muscle uses about 6 calories a day as opposed to each pound of fat, which burns about 2 calories a day. Over time, it all adds up.

Drink more water. Your body needs water to burn calories. One study found that adults who drank eight or more glasses a day burned more calories than those who drank just four. Another found that cold water, as opposed to room temperature water, raises your resting metabolism by as much as 50 calories a day. Iced tea or iced coffee (with lots of ice cubes) will do the trick, too (provided you don’t load it up with cream and sugar!)

Eat more often. (not MORE, but more OFTEN).  That’s because eating small meals or snacks every 3 or 4 hours keeps your metabolism churning as opposed to eating large meals with many hours in between. And some studies support this concept further by finding that people who snack regularly eat smaller amounts at mealtime.

Pick protein. The body works harder if you eat protein: it burns up to twice as many calories digesting it as it does digesting carbohydrates or fat. To keep your diet balanced, don’t eliminate carbs entirely. Instead, try replacing some carbs with lean, protein-rich foods.

Don’t crash (diet). Severely cutting your calories may peel off the pounds, but it does that by taking it off your muscle. And remember: the lower your muscle mass, the slower your metabolism. Your new, thinner body won’t stay that way for long, unfortunately. Its metabolism will now be even slower than before, so chances are good that you’ll gain back the weight – and then some.