Originally Answered: I am trying to lose body fat and build lean mass.
You've got the right idea: it's critical to increase your lean muscle mass, which is your metabolic furnace that will burn extra energy 24 hours a day. If, for example, you add 10 pounds of muscle in the next six to twelve months, your body will burn an additional 350 to 500 calories daily.
If you want to lose fat in a lasting way, I recommend adopting a program with three parts, namely, (1) strength training, (2) eating well, and (3) mild cardio. I'll give you the outline here and you can find important details on all three parts by using the links below.
It's best to get your physician's blessing before altering your physical habits in a significant way. Also, don't try to do everything at once. Adopt one piece of the program and use it for 3 to 10 weeks until it seems normal and habitual. Then adopt another piece. If you try to change everything at once, you are likely to wind up with no lasting results. So, be patient. Think of yourself as adopting a sustainable program that will yield positive results from now until your dotage.
(1) Do a whole body strength routine. Concentrate on using only the basic compound exercises, namely, full squats, deadlifts, presses, rows, dips, and chins. Learn perfect exercise technique and use it on every rep.
Once you are training with intensity, you'll experience DOMS (delayed onset muscular soreness) afterwards. Wait 24 to 48 hours before training again in order to ensure systemic recovery.
Remember: you don't grow in the gym. What you do in the gym should stimulate growth during the recovery phase. So get plenty of rest and sleep.
In practice, this means you'll be doing strength training for about 45 minutes one afternoon every 4 or 5 days.
(2) To maximize your results from strength training, it's critical to eat well every day.
Have a meal about every three waking hours and never skip a meal. Each meal should contain sufficient proteins from natural sources. 'Sufficient' means at least 20 grams each feeding for a male and 15 grams for a female. Natural sources are foods such as game and grass-fed meats, fish that are not from fish farms, and organic eggs. Avoid dairy products.
Drink plenty of cold, clean water. Individual needs vary. I suggest starting with 3 quarts daily.
Do not consume any unnatural (processed, refined) carbs. Also avoid beans and potatoes. Instead, you may have up to 75 grams of carbs daily from natural sources such as (preferably organic) vegetables and berries and some other fruits.
By itself, eating in this way will boost your metabolic rate.
(3) Cardio will burn extra energy both during and after exercising. The best mild cardio is brisk walking. 'Brisk' means walking at a 4 mph pace.
To use walking to lose body fat, you'll need to average walking 3, 4, 5, or even 6 miles daily. You may break your walks into more than one session. The best time to walk is before your first meal of the day.
Once you have regained your desired percentage of body fat, you should continue to walk 2 miles daily, which will help to avoid getting fatter.
If you haven't been walking, go slowly at first! Each time out, just increase your distance a little bit until you are able to walk, say, 3 miles at a comfortable pace. Then increase your pace until you are covering that distance in just under 45 minutes. Then, if you want, you can add in another mile.
Use walking shoes that are less than 6 months old; do not use running shoes or cross trainers. You'll find other tips on the website including tips on warming up for both walking and strength training and safety tips for walking and strength training.
Since cardio is boring, I find it help to listen to an audio program when I'm walking. Unlike cardio, strength training is fun! I enjoy listening to upbeat rock music during it.
If you work this program, it will work well for you, Don.
Train in good health.
All my best wishes.