"I started running/bike riding everyday and after 3 weeks instead of losing weight I have gained 5 pounds! WHY????"

There are a few things that can cause you to gain weight,when you’re exercising,the least likely based on what you’re doing is muscle gain,though a minute amount can be gained in that time,but no way did you gain five pounds of muscle in that short period,especially biking and running,so let’s rule that one right out.

 

You’re staying well hydrated,which is usually the best way not to retain water,but if you’re sweating profusely and not drinking enough during exercise,your body WILL hold water.This is a defense mechanism built into all of us.

 

On to more defense mechanisms.You’re burning calories while you’re exercising,but apparently eating a little less.Your body is certainly storing mre muscle and liver glycogen,in preparation for the next session.You should be snacking!

Eating 5-6 times a day,but much smaller servings will help your body better regulate blood glucose and also not have your body "believe" that there’s no more food around the bend.This will cause you to store more  fat.Leaning on more protein than fats and sugars has a dual benefit:

 

Protein has a higher thermic value than the other two macronutrients.This has a metablic advantage for you.

Protein can be converted to glucose via gluconeogenisis,as fat can be through ketosis.Your body will always think there’s sufficient caloric intake provided you continue to feed it,and protein would be one ofthe best foods to do so.

 

Do you care what you weigh,or how you look?

If asthetics are the issue,STAY OFF THE SCALE!How much you weigh has little to nothing to do with what you weigh.Use a mirror to guage your progress,unless you need to lose weight for medical reasons.

 

You need to put together a proper diet plan,so here’s an excerpt from one of my old answers.

 

 

 

This is how I help to keep my weight in check,lose weight before a competition (more to it than I'll post here-but this would be a temporary fix) and ensure that I eat healthy foods.My diet is different,but so are my goals.I'll give you these guidelines.

 

Doing strength training first,then your aerobic work is far better,because:

Strength traing depeletes gycogen (stored carbohydrate),then you can focus on burning fat during the aerobic work.Strength tarining also increases lean body mass (muscle) which is far more metabolic than any other type of tissue.

 

Diet has recently been shown to be more effective than exercise,for weight reduction,but a combination of both is best.Pay careful attention,this says "healthy" diet.

 

 http://health.yahoo.com/news/healthday/healthydietsbeatexerciseforweightloss

 

Now a healthy diet consists of a balance of all of the importamt nutrients and macronutrients.That boils down to eating 5-6 small meals per day,over the customary 3.

 

 

The reason for splitting your meals into smaller portions is to control the rise in blood glucose (blood sugar).When blood glucose exceeds a certain level insulin is secreted to control the BG levels.At this point one of two things will happen.Insulin will transport the glucose to the liver andf muscles,to be stored as glycogen,or convert it to fat and store in in adipose tissue.

 

So eating lower glycemic vegetables,more protein(thermic effect) and beneficial fats are the key,along with portion control.Glycemic index.

http://www.southbeach-diet-plan.com/glycemicfoodchart.htm

Here’s where you figure that out.Count your calories and base your daily caloric intake on your BMR,which can be calculated here

 http://www.bmi-calculator.net/bmr-calculator/

Next,water.This is a new clinical study conducted on water and the rise in metabolism.

 http://www.webmd.com/diet/news/20040105/drinking-water-may-speed-weight-loss

 

I am not an exercise physiologist but I have taught exercise from time to time and have exercised/eaten well all my adult life. My answer is based on experience and knowledge I have picked up along the way.

First, don't watch the scale; watch what is happening to your body. Are certain areas building muscle? Do you appear leaner? Do your clothes fit better? Muscle weighs more than fat.

Second, it is summer and warmer temps may be causing you to retain water. Especially if you are drinking more––which you should be––your body has a natural inclination to hold onto that water more in warm weather. You'd be surprised how a major drop in temps in the summer can cause a weight drop of several pounds as well.

Third, "I eat well" means different things to different people. Are you loading up on carbs because of your exercise? At 53, believe me, I've heard it all about what is the healthiest way to eat and what I finally settled on is that everyone's body is different and you have to do what works best for you. Bread, for example, is a no-no in my diet if I want to stay at a good weight. So I get my carbs in other ways, like cereals.

Fourth, I'm not sure who told you that you needed to lose ten pounds. I hate to say this, but sometimes you need to be skeptical even of the medical community on this one because trends change. Ten pounds isn't morbidly obese and could just be your natural body weight. If you eat right and exercise, and if you feel better, you could be turning fat into muscle––nothing wrong with that. If you are really doing everything right, a doctor shouldn't hound you to lose that weight, because you may end up doing something wrong like cutting back on essential nutrients.

Finally, if you have just started an exercise program, I'd advise against running. If you are out of shape, you can injure yourself badly. Bike riding is good, but instead of running, walk. If you over do the exercise you could tire yourself out so that you have no energy for anything else the rest of the day. You could actually end up using less calories.

Nuff said.

You're probably initially adding muscle (tone) faster than burning off the fat.  Muscle weighs more the fat so at first you may gain weight.  The good part is that eventually you will be burning more calories (and fat) even at rest (ie sitting, even sleeping) due to the added muscle. 

That's why it is better to think of exercising for body/muscle tone, stamina and strength rather than for "losing weight".    Keep on exercising -- it's really about how you feel in terms of physical heath and what you see in the mirror rather than what you see on the scale.

P.S.  Since the disclaimer is everywhere, I'll modestly suggest that you also talk to your physician or "health care professional" to make sure your physically ready for the challenge of your exercise routine.