It seems like body fat accumulation has become a hobby for many. It's a very simple process. First, you consume a large amount of high-calorie, low-nutrient foods. Then you bust your butt at not being physically active. BOOM! You're in the fat accumulation club. It's where biochemistry meets a lack of discipline. 
 
If you want to reverse the process of body fat accumulation, you can do it if you take a sensible approach. It's not easy, but you can do it if you shore up your diet, eat better food, and create a calorie deficit. That is the hard part. Many fail at this step because they overeat and thus create a calorie surplus. The end result of this is fat weight gain.
 
You also need to implement appropriate exercise that builds muscle and indirectly targets adipose fat stores (the stuff you can pinch). That is actually the easy part, but many fail here because they think "exercise" means plodding away on a treadmill for 45 minutes or partaking in a Yoga class three days per week. Both of the aforementioned are poor options for optimal fat loss.
 

Focus on More Than Scale Weight

The general consensus for losing scale weight is a calorie deficit: Consume fewer calories and engage in traditional low-level "cardio" workouts. Conversely, the general consensus for gaining scale weight is a calorie surplus: Consume more calories and engage in strength training to stimulate muscle tissue growth. Both would work, but we're talking scale weight only, independent of your fat-to-muscle ratio, which should be the focus.
 
You can lose scale weight and yet have a higher fat-to-muscle ratio. That is, you may weigh less, but you possess more fat and less muscle, proportionally. You will not look better. This is what happens to many cardio fanatics, who solely run for miles and fail to strength train. They are lighter on the scale, but have no shape.
 
You can gain scale weight and yet have a lower body fat-to-muscle ratio. That is, you may weigh more but possess less fat and more muscle, proportionally. That should be the goal because muscle is sexier than fat. The former is not ideal, and the latter represents the better option: Less fat + more muscle = a better-looking physique, independent of scale weight. 
 
scales only tell part of the dieting story
The scale only tells part of the story. 
 

Genetics and Body Types

Your body shape is primarily determined by your skeletal structure and inherent muscle mass. On one end of the continuum, there is the ectomorph, which has proportionally less muscle mass and low body fat—the skinny type. On the other end is the endomorph, which as proportionally less or average muscle mass and high body fat—the thick and obese type. The optimal, "in the middle" body type is the mesomorph. This person is muscular, stocky, and low in body fat. 
 
The truth is that it is very difficult to alter your natural body type (tall and thin vs. short and thick) without major surgery. But you can alter the size of your muscles and the amount of fat on your body. That is, your body composition can be altered, and you can change your looks within the confines of your genetic inheritance.
 

The Climb Gets Steeper

That should be the sensible approach to fat loss. However, one reality hardcore fat loss seekers need to embrace is that it becomes more difficult to only burn stored adipose fat as you become leaner. That is, the less fat you have, the more the body will go after other sources of energy, such as your existing muscle mass and non-fat substrates.
 
Take a person who has 30% body fat. They have more fat to use as an energy substrate in the beginning stages of a fat loss program. With a proper calorie intake and appropriate exercise, they can better target fat stores while sparing muscle tissue as an energy source. 
 
Take a person who has 15% body fat. They have less fat to use as an energy substrate, and will find it more difficult to use only adipose fat as the sole source of energy. It’s a steeper climb as you become leaner and have less stored fat to utilize as energy for two reasons:
 
  1. Your body’s survival instinct is to preserve fat stores for future use. When it senses a calorie deficit and higher energy demand, it will favor preservation over depletion.
  2. There is a limit to the rate at which your body obtains energy from fat. The greater the amount of fat you lose, the slower your rate of fat metabolism will be. 
 
Let’s recap the basics. For proper fat loss, one needs to:
 
  • Create a calorie deficit.
  • Strength train to build (or at least preserve) muscle tissue in the wake of that calorie deficit. 
 
Accept the limits of your body type. If you are tall and thin, have wide hips, narrow shoulders, are pear-shaped, or apple-shaped, you can only alter your fat to muscle ratio within those confines. Understand the climb to less body fat gets steeper as you become leaner. Those last 10 pounds are much more difficult to lose than the first 10 pounds.
 

How Long Will It Take?

What is the time frame for sensibly losing a reasonable amount of body fat? We know that there are approximately 3,500 calories in one pound of body fat.1 The average person can only lose fat at the rate of approximately 30 calories per pound of body fat per day.2
 
From that, there is a reasonable formula developed by Drew Baye:
 
 [(X1 - X2) x 3,500] / [(X1 + X2) x 15] = D
 
Where:
  • X1 = your initial body fat (in pounds).
  • X2 = your end-goal body fat (in pounds)
  • D = The approximate number of days to reach your end body fat goal if you create a daily caloric deficit equal to your current amount of body fat (in pounds) multiplied by 30.
 
Here is an example of a person who wants to reduce their body fat percentage from 30% to 20% without reducing lean body mass:
 
  • Scale weight = 190lb
  • Current body fat percentage = 30%
  • X1 = .30 x 190 = 57lb of fat
  • 190lb – 57lb of fat = 133lb of lean mass
  • 20% body fat = 133lb x 1.2 = 160lb
  • X2 = 160lb – 133lb lean body mass = 27lb of fat
 
Let's plug the numbers into the estimated formula:
 
[(57-27) x 3,500] / [(57 + 27) x 15] = 83.3
 
Therefore, it would take approximately 84 days of a diet with optimal caloric balance for a 190lb person with 30% body fat to reduce to 160lb and 20% body fat.
 

The Climb Gets Steeper as You Get Lower

Losing body fat becomes a "steeper climb to the bottom" as you become leaner. To obtain your goal, you need to remain dedicated to a quality diet, precise calorie intake, and an emphasis on muscle-stimulating strength training.
 
There is a hormonal driver of your overeating:
 
References:
1. Hall, Kevin D. "What is the required energy deficit per unit weight loss?." International Journal of Obesity 32, no. 3 (2008): 573-576.
2. Alpert, Seymour S. "A limit on the energy transfer rate from the human fat store in hypophagia." Journal of Theoretical Biology 233, no. 1 (2005): 1-13.
 
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