How much weight can I lose and in what time frame from walking on a treadmill?

How much weight should in what time frame can i lose walking on a treadmill at 3.4mph for 45 minutes 6 days a week ? i am a 39 yr old female
"K"
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Gary advises:

Unfortunately there are too many factors at play to be able to give a definite answer to your question. But I do have some comments and recommendations for you.

Weight lost slowly is weight least likely to be regained.
If you lose just a kilo a week over several months as opposed to several per week for a month, then you are most likely to keep that weight off. This is because the gradual weight loss is the result of subtle changes in daily behaviour that are sustainable.

Think about lean and fat weight.
When losing weight, you want to be losing fat and not lean tissue including muscle. As one gets older, one of the best measures of health and vitality is lean weight. If you are on an exercise programme you want to be doing one that increases lean weight while getting rid of excess fat weight.

A kilo of fat takes up much more volume than a kilo of muscle.
This explains why a fit, lean person sinks and an unfit, fat person floats. If you are on a balanced health and fitness programme, it is possible and often desirable that you will gain a kilo or two in weight during the first 6-8 weeks. This is because weak and wasted muscles will respond to the unfamiliar exercise by getting larger and harder.

Lean tissue burns fat.
As your lean weight increases, so does your ability to burn fat during exercise and even at rest. This explains why a fit and toned person has a more stable body weight than their unfit equivalent. After 6-8 weeks the participant in a balanced fitness programme should notice a steady decline in overall body weight. This is because the initial gain in lean muscle levels off while the steady loss of body fat that was initially masked by the lean weight gain continues and even accelerates.

The best measure of success is not weight.
The best measure is body dimensions and your feelings of energy and vitality. Use a tape measure to compare loss of girth about the thighs, hips, tummy and chest. How clothes fit are a good measure. Think about how quickly you skip up the steps to home, rather than how much you weigh. Thin is not always healthy.

Walking is a wonderful exercise but not enough on its own. You need to add upper body exercise in the form of lifting weights from the ground to above the head, if you are not doing so already. Walking is great for the circulation and the muscles from the hips down. Do not neglect the muscles and bones from the hips up. Think of a balanced workout for the entire body.

Do not fall into a pace and distance rut.
What I mean by this is do not walk at just 4.5km/hr for 45 minutes every day. The body is inherently lazy and it will quickly get lazily used to the monotony. “Ho-hum: another 45 minute plod – time to go to sleep”. You must keep surprising your body by mixing up your sessions. Never do the same thing two days in a row. Do a short, fast walk today. Make the next a long two hour one. Then the next can be short with hills. Keep your body guessing about what is going to be thrown at it. Keep it on its toes and it will respond by getting stronger and stronger instead of falling asleep on the job. Got the idea?
Walk outdoors and get healthy.
Save the treadmill for the really nasty weather. Do every walk you can outdoors in true outdoors Kiwi tradition. It is healthier. Suck in the fresh air, get the bright light on your face, listen to the birds, and admire the views. Go with your friends; make every walk an adventure of discovery. Walk different suburbs and admire the gardens. Explore the trails about the city outskirts, walk the Tongariro Crossing. Save what you would spend on the gym and walk the Inca Trail of Peru next year.