Control serving sizes to reduce your calories.
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Whether you're dieting for a special event or some sort of physique or fitness competition, or just to give yourself something to aim for, 90 days is a long enough time to really notice a difference in your body fat levels. Body fat percentage is an accurate indicator of your health and fitness, notes dietitian Tracy Daly of San Diego State University.
Calculate Your Calorie Needs
Calculate how many calories you need each day. To maintain weight, you need about 15 calories per pound of body weight, according to the Harvard Medical School, so to drop fat, you'll need to go slightly below this. Start with 12 to 13 calories per pound and go from there.
Consider Your Day to Day Activity Levels
Factor in your activity levels when working out your calories. According to the American Council on Exercise, your resting metabolic rate makes up around 60 percent to 80 percent of your calorie burn each day. While this is determined mainly by genetics, a large proportion of the rest of the calories you burn comes from exercise. If you're highly active, you can eat more calories while still losing fat, but if you work a sedentary job, or do little exercise, you'll need fewer.
Burn Cals at the Gym, Too
While your daily activity is the largest contributor to your calorie burn, you'll also need to work out to burn excess calories. Schedule in four to five one-hour sessions of cardiovascular exercise a week for weight loss, and strength train two to three times weekly to build lean muscle. Make sure to use one day as a rest day, which gives your muscles a chance to recover.
Pump Up the Protein
Increase your protein intake. Protein helps fat loss in two ways. First, it aids in muscle mass retention, and if you're dropping weight but maintaining muscle, you can be sure that the weight you're dropping will be fat mass, not lean mass. Second, your body requires more energy to store protein and build muscle, so your calorie burn is higher. Dr. David Heber of the UCLA Center for Human Nutrition advises getting around 20 percent of your daily calories from protein-based foods.
Practice Portion Control
Make your portions smaller. Energy balance and calorie control does come down to how much goes in versus how much goes out. By far the easiest way to make sure you're not overdoing the calories is to cut back on your serving sizes, particularly when it comes to higher-calorie foods.
Schedule Weekly Weigh Ins
Weigh yourself once a week. Stepping on the scale may not provide body fat levels, but it gives a good indication of progress. If you're maintaining strength in the gym, you can be sure you're maintaining muscle, so the weight you're losing will be body fat. Between 1 and 2 pounds per week is a good weekly weight loss, according to the National Heart, Lung and Blood Institute.
Bust Through Plateaus
Reduce your calorie intake when you hit a weight loss or fat loss plateau. Most people hit plateaus when losing weight, according to dietitian Lorraine Matthews-Antosiewicz, so you will hit a stumbling block from time to time. If you don't lose weight one week, drop your daily calories by 50 to 100. Over 90 days, you may end up reducing your calories two to three times.
Document Your Progress
Take a progress photo at the beginning and end points of your journey and at the halfway mark. Take one shot from the front, one from the side and one from the back while wearing a bathing suit. Use the first one as motivation, the second as a progress assessment and the final one to show how far you've come.
Items you will need
Ask a qualified fitness professional to take your body fat percentage measurement using callipers on day one and on day 90. You can use an electric body fat monitor if you wish, but callipers provide a more reliable reading, notes Daly.
Include both weight training and cardio in your routine -- cardio will help burn fat, while weight training preserves muscle mass, thus ensuring a higher percentage of your weight loss is fat.
Check with your doctor before starting any new routine.