Weight loss can be an extremely challenging and frustrating process. People embark on diets - and / or exercise programs - with a lot of optimism, and derive satisfaction and the motivation to continue when these interventions realise rapid initial weight loss successes. This is invariably followed by a weight plateau in spite of maintaining the reduced diet / increased exercise regimen, followed by a loss of motivation, reversion to pre-programmatic diet / exercise levels, and weight regain that may often go above the baseline that one started with.
Why does this cycling of weight happen? And how does one break out of this cycle? An understanding of the science behind weight loss is critical to figure out the reasons behind this and construct a weight-loss program that actually works.
The Science
When you go on a diet, or increase physical activity to burn more calories without replenishing these calories through increased food intake, the body is faced with a deficiency of calories, leading to reduced availability of glucose in the blood. To address this deficiency, the body must tap into its various nutrient stores:
- Stage 1: Glycogen:
- The first, and most easily accessible store of nutrients available to the body is glycogen, a type of carbohydrate stored in the liver and muscles. The liver's glycogen stores - about 30% of the total glycogen in the body - are depleted rapidly, while it can take several days or weeks to to tap into most of the glycogen stores in muscle tissue.
- The body's glycogen stores are limited - only about 600 grams, or 2,400 kCal - sufficient to meet the body's energy requirements for 1-2 days.
- Each gram of glycogen is stored with 3-4 grams of water, so when the body converts glycogen into glucose, the body loses weight primarily through water loss. This is why diets lead to rapid initial weight loss.
- Stage 2: Fat
- Once glycogen stores are depleted (and assuming a continued caloric deficit) the body turns to stored fat in adipose tissue. A 70-kg healthy adult male has fat stores of 10-15 kg. Because fat is energy dense - each kg of stored fat provides 7,700 kCal of energy - these fat stores are sufficient to provide several weeks to months of energy supply requirements
- When fat becomes a significant source of the body's energy stores in response to dietary calorie deficiency, the rate of weight loss reduces, given the energy density of fat.
- Stage 3: Muscle
- After an initial stage of tapping into stored fat reserves, the body decides to conserve fat as a survival mechanism; and turns to its muscle stores for energy. Muscles are broken down into amino acids which are converted into glucose. This loss is intensified when the diet is protein deficient and when muscle mass is not replenished via exercise (strength training)
However, this is not the end of the story. As the body loses muscle mass, its metabolic processes slow down, reducing demand for calories. When this happens, weight loss plateaus, because the body has reached a new calorie intake-expense equilibrium. Following this plateau, human nature takes over, leading to a loss of motivation, a reversion to pre-diet / pre-exercise behaviours, the rebuilding of the body's fat and glycogen stores, and, unless muscle mass is also replenished through exercise, a poorer fat to muscle ratio and a subsequent tendency to gain even more weight.
Tips for Sustainable Weight Loss
Having understood the science, if you want to successfully and sustainably lose weight, here are our top tips:
- Long-term commitment - The body is stubborn, and will not give up its fat stores without a fight. To win this war, you have to be prepared for the long-haul - there is no overnight success here
- Achieve, and be prepared to sustain, a calorie deficit relative to your baseline over a period of years, if not permanently. Also remember that your calorie needs reduce as you age, so keep adjusting four calorie intake downwards over the duration of this war
- Invest in continuous replenishment of muscle mass through strength training combined with adequate protein intake. Otherwise, your body will reach a reduced calorie equilibrium by adjusting its fat to muscle ratio.