60-90 minutes of exercise daily

I dont have any printed materials. All I can offer is some hearsay.
I was once told that your body only starts to burn fat after about an hour of exercise, prior to that your body is accessing the quick burn sugars it has stored.

I find this interesting. I was 100 pounds overweight and started by changing what I ate. I lost 2-4 pounds a week to start and did no physical activity. When I added excercise some 4 months later my weight loss slowed. After a year of losing weight I started tri training and my weight loss stopped. Now I work out 6-10 hours a week and eat better and barely lose any weight.

I think that everyone needs to find out what works for them and it isn't the same for everyone.

 According to Ken Mierke's book "Triathletes Guide to Run Training"

"the first 20 min of exercise the primary source of energy is carbohydrates.  After approx one hour of exercise at fat burning intensity the body secretes greater levels of cortisol.  This increases fat burning dramatically."

So you have to exercise at least 20+ min straight to start training muscles to burn fat and going much longer is expotentially better.

I would like to add a few points that may be helpful. No I'm not a doctor,(although I have played one on TV and I have stayed at a Holiday Inn Express) but I have lost a considerable amount of weight and I'm currently losing even more in preparation for this season.

1. Get a checkup before doing anything. I feel like too many diet and exercise routines target younger and relatively healthy folks. I was a 50 y/o diabetic with high blood pressure and a list of maladies a mile long. Get a checkup and a stress test if possible.

2. Forget the fads. I've tried them all and they don't work. What you learned in elementary school was the truth. A diet low in fat, calories, and exercise will result in weight loss.

3. No one here has mentioned Resting Energy Expenditure, ie the calories it takes for your body to keep you alive and you will burn these even if you stayed in bed for 24 hours. REE is dependent ,for the most part, on you body weight. Ding,ding,ding, you guessed it. The more you weigh the faster you will lose those initial pounds. But if your not careful you'll level out before reaching your goal. As you get smaller the diet either has to get even more spartan or the exercise must increase. Cals in/ cals out. When I started my diet my REE was over 2400 cls/day. Now it's around 1500. Well If my diet or exercise strategy didn't change I'd never have lost another pound. 900 cals is a lot of miles or a lot of lettuce.

4. As for caloric intake there is only one rule for weight loss. The gozoutas must be more than the gozintas. An earlier writer was right when they stated that a lb of weight is 3500 cals. It's simple math.

5. Slow exercise gets the best calorie burn. By that I mean for the beginner, assuming a previous sedentary lifestyle. Think of it this way. Slow exercise allows the body time to reduce fat to energy and you lose fat, not lean body mass. The faster your heart rate the quicker your body begins to go after fuel so it begins to use blood sugar, liver glycogen, lean muscle breakdown,etc. That is not your goal. You want to be an athelete not a bone covered in fat. So what's slow exercise.Ahhah

6.The heart rate monitor becomes more important than all the diet books combined. Get on your workout clothes, your favorite excercise shoes and strap on your heart rate monitor. They are less than 50 bucks and they are the key to proper weight loss. After determining your Maximum Heart Rate (220- your age)(There's a huge thread on this but for our level this is all you need) Multiply that number by .65. 65% of MHR is prime fat burning territory. Walk, jog, cycle, treadmill, whatever just DO NOT go above this level.

7. As the weight comes down you must either increase the exercise or further reduce your caloric intake. If you lose a lot of weight you'l soon find yourself running, cycling, working out or whatever for 90-120 minutes a day. Now's the time to venture into one of the BT training regimens which will help with your aerobic/anerobic/, endurance, or strength needs. 

8. Never buy into the old "I've replaced fat with muscle so that's why my weight hasn't changed" thing. Muscle per mass weighs about 1-2% more than fat. If your weight loss has plateaued then try this. a. Seriously review your current REE, caloric intake, exercise, and WATER intake. If these are fine, and you must be honest with yourself, then you might want to:

Get off the diet for a week. Eat. Eat some more. Then eat some more. Trick your body a little. Then go back to the diet and exercise with a vengence.

Hope this helps. I've lost over 55 lbs, no diabetes, no high blood pressure, and doing triathlons.

BTW, hang in there and always, always support one another.

I think the idea is to increase the duration as much as possible and decrease the intensity as much as you need because, just by slowing down, you can go a lot longer and burn more total calories.  If you can run 15 minutes, you can probabaly walk an hour easily.  Walking an hour would burn about double the calories of jogging for 15 minutes.  That is the equation at work behind the recommendation.  If you were the government, you could measure each individual's capacity to run/walk/bike/swim and then give them a personalized recommendation for their exercise or you could just assume most people would be better off with the one hour of brisk walking recommendation but aren't going to do anything you recommend anyway, ergo the 60-90 minute headline.  If you search for and read the entire government recommendation, (I haven't this time but I have in the past), there is usually some qualitative advice about how both intensity and duration affect the response but it is dumbed down to the point of being useless.

The truth is you need to exercise just a little bit below the amount you can recover from each day and your mileage may vary.

TW

These studies are the kinds of things that really need to be studied and fully broken down into its parts to understand.  Unfortunately, it seems like most of society will simply see the catchy headline, "You must do 90 minutes a day to lose weight" and move on.  Not only is that ridiculous, it seems HORRIBLY discouraging to people who want to start.  I work out a lot, and I don't have time to work out 90 minutes a day.  The average person who wants to try to do something about their weight has enough obstacles and doesn't need this kind of thing to discourage them. 

Regardless of how true the information may be, I wish it was presented in a better way.  Something like, "Although beginners will benefit from any increase in physical activity and should not be expected to engage in this much activity due to the chance of injury or fatigue, studies have shown that significant weight loss is best achieved.....blah blah blah.....so on and so forth."

I think I found the report in PDF st this link:

http://www.health.gov/dietaryguidelines/dga2005/document/

The actual phrasing in the report is:

up to 60 minutes of moderate- to vigorous-intensity physical activity per day may be needed to prevent weight gain, but as much as 60 to 90 minutes of moderate-intensity physical activity per day is recommended to sustain weight loss for previously overweight people

Of course the press when leaves out the words "up to" and "as much as" when they reprt on the report

What Gullah and a few other folks have said: in order to lose weight you gotta consume fewer calories than you use. The problem is that exercise simply doesn't increase your caloric expenditure enough to make a huge difference, especially the level of exercise that a significanly overweight person would most likely engage in.

Exercise is great for improving and maintaining overall health, and it is useful for weight loss but you'll lose weight quicker, or at least slow down your weight gain, by giving up the daily bowl of ice cream than spending 30 minutes on a treadmill.

If your husband is at all of the geek persuasion, he may find the website below useful:

http://www.fourmilab.ch/hackdiet/