Here’s why you’re still not losing weight in a calorie deficit

Dr Nick Fuller
Leading Obesity Expert at the University of Sydney and founder of Interval Weight Loss.

Have you found your weight loss has plateaued? It's not a lack of willpower; it's biology. Your body's physiological responses prevent further weight loss and lead you to put it back on.

Dr Nick Fuller is from the Charles Perkins Centre at the University of Sydney and author of the Interval Weight Loss program. He sheds light on how your biology prevents you from succeeding and what you can do to ensure long-term weight-loss success.

1. Metabolism

Your metabolic rate is how much energy you burn at rest. It is determined by how much muscle and body fat you carry. Muscle is more metabolically active than fat (i.e. it burns more energy than fat). A person with a higher muscle mass will have a faster metabolic rate than someone of the same bodyweight with a higher fat mass.

With weight loss, your metabolism will decrease because your body mass decreases. However, there is a decrease in your metabolism by a further 15 per cent beyond what can be accounted for by a reduction in body mass. Meaning that for every diet you attempt, the rate at which you burn off your food slows by 15 per cent. Worse still, research has shown that your metabolism doesn't recover even after stacking the weight back on.

Tip: Exercise plays a critical role in preserving your muscle mass when you’re losing weight. Find activities you enjoy and can stick to them long-term.

2. Energy source

At rest, your body is predominantly burning fat stores. However, when you lose weight, your body will start to work differently. It will shift the energy source you use from fat to carbohydrates to ensure your body holds onto its fat. You will burn less energy at rest, and you will regain the weight you lost.

Tip: Keep yourself accountable by jumping on the scales once per week and monitoring your weight trend over time.

3. Appetite hormones

Your appetite hormones play a large part in ensuring your day-to-day weight stays stable. For example, when you are hungry, the stomach releases a hormone called ghrelin to tell the brain to tell you to eat. When it's time to stop eating, other hormones are released from both the gut and body fat tissue to signal that. But when you’re losing weight, these appetite hormones will work differently. They will suppress your feeling of fullness and tell you to eat more.

Your body begs you to binge when you deprive it of food. Even after you have regained the weight you lost, your appetite hormones do not return to the same levels they were before dieting. Which means you will continue to feel hungry after stacking the kilos back on.

Tip: Don't deprive yourself of food when you’re trying to lose weight; eat more, not less, and give your body the nutrition it needs.

4. Autonomic nervous system

The autonomic nervous system regulates body functions like heart rate and breathing rate. It consists of the sympathetic and parasympathetic nervous system. The sympathetic nervous system is referred to as the 'fight or flight' system, and the parasympathetic nervous system is called the 'rest and digest' system.

The systems work to oppose one another, whereby one will activate a physiological response and the other will inhibit. Your metabolism will slow down when you lose weight. Your heart rate and breathing rate will also decrease as the parasympathetic nervous system takes control.

Tip: To prevent your metabolism slowing, impose "intervals" every second month to allow your body the rest it needs.

5. Thyroid gland

The thyroid gland is the gatekeeper to your metabolism. A healthy thyroid means your metabolism is firing. A sluggish or poorly functioning thyroid implies the amount of energy you should be expending will be compromised. Under normal circumstances, your thyroid gland will produce hormones. But when you restrict the amount of food you eat, fewer of these hormones are secreted, which reduces the amount of energy you burn at rest.

Tip: Forget calorie counting. Instead, load up your plate with a wide variety of colours and slow down your consumption by using chopsticks or a teaspoon.

6. Adrenal gland

The adrenal glands produce a range of hormones, including the stress hormone cortisol. When stressors like dieting are imposed on the body, the pituitary gland stimulates the release of a hormone, producing cortisol. An excess of cortisol production leads to weight gain, and when you restrict the amount of food you eat, the cortisol level in your blood increases.

Tip: Set a goal that is a lifetime event rather than a moment in time. The all-or-nothing approach and the 4, 8 or 12-week weight loss programs don't work long-term.

7. Brain function

Typically, diets tell us to restrict certain foods to create a calorie deficit. However, limiting or cutting out certain foods or food groups on a diet changes brain function. There is a reason why you start craving the morning toast the exact moment you decide to eliminate bread. It is because of heightened activity in the reward-system part of the brain.

You give in to your cravings because those foods release the feel-good chemicals called endorphins. They also release the learning chemical called dopamine, which remembers that feel-good response the next time you see it. But that's not the full extent of it.

Another significant change that a person will experience when dieting is reduced activity in a very clever part of the brain called the hypothalamus and other areas involved in the emotional control of food intake. The result is decreased control of food intake and impairment in sensing a positive energy balance following dieting.

A psychological response dubbed the 'what-the-hell effect' is then triggered. This response is a vicious cycle of indulgence, followed by guilt, followed by greater indulgence. You end up eating the whole packet of Tim Tams instead of just the one.

Tip: Don't deprive yourself entirely of your favourite foods. Wean yourself off them slowly and aim to include them just once per week.