Will Extreme Weight Loss Slow Your Metabolism?

Do you feel like you’re losing the weight loss battle? Constant setbacks can cause people to turn to drastic measures to achieve their goals. Repeated use of drastic measures to lose weight may lead to the loss of not just the battle, but the entire war on weight loss.

Weight Loss & Your Metabolism

Dietary restriction and increased physical activity can cause short-term weight loss, but many people find that they regain the weight they have lost. This is especially true for individuals who have gone through weight loss programs or fad diets that produce extreme or rapid weight loss. Current research suggests that maintaining the reduced weight over the long-term will require more support than just diet and exercise intervention alone.

A vast number of factors influence body weight, but this blog will focus on only a few. Individual genetics do play a role, as well as early life experiences and parental influence. The body’s internal neuro-hormonal system, behavioural processes, as well as the external environment also contribute to body weight regulation.

First, it is important to lay out the four components of an individual’s total daily energy expenditure:

1. The basal metabolism makes up about 70% of the total calories the average person burns in one day to sustain basic cellular function, organs, muscles and body systems to simply survive.
2. On top of this there is unplanned activity (about 15% of our total energy expenditure).
3. Planned exercise (about 10% of our total calories burned one day on average).
4. The last 5% of total energy expenditure comes from the body using energy to digest and process food into energy (called the thermic effect of food).

Weight Loss Affects Metabolism

The complexity of physiological adaptation to weight loss is enormous and still requires more clarity through further research. A component of this physiological adaptation is what’s called “metabolic adaptation.” The metabolic adaptation resulting from weight loss is a persistent slowing of resting metabolic rate and other factors that favour weight regain.

The hormonal fluctuations that seem to synergistically promote weight regain when there is energy restriction and lowered body weight include:

• Lowered leptin levels (leptin promotes the feeling of fullness) and higher Ghrelin levels (promotes higher hunger levels). This causes a physiological drive to increase food intake.
• Lower insulin levels (a hormone that allows the body to use nutrients for energy and building tissue) due to lower food intake which causes a decrease in energy availability and causes one to reduce planned physical activity resulting in a loss of lean body mass. This will reduce metabolic rate and energy expenditure.
• Lower testosterone which may be linked to a disruption in body fat regulation and reduced muscle mass. Since muscle burns energy, this also reduces metabolic rate.
• Lower thyroid hormones leading to a disruption in metabolic rate favoring weight gain.
• Higher cortisol levels (a stress hormone) that leads to increased muscle breakdown. This also reduces metabolic rate.

Many of these changes in hormones result in a drop in lean body mass. However, there is evidence to suggest that extreme weight loss can result in a persistent drop in metabolic rate that is beyond what is explained by loss of lean body mass. In fact, a study done on Biggest Loser participants indicated that resting metabolic rate was substantially lower at the end of their weight loss competition – despite a relative maintenance of lean body mass. On top of this, the metabolic adaptation persisted for multiple years after the competition.

Studies have shown that on top of the hormonal changes and loss of lean body mass, changes in the way mitochondria function seem to promote weight regain. Mitochondria are structures in each cell that help generate energy (in the form of ATP) for the body to use as fuel for metabolic functions, digestion of food and physical activity. In weight loss, mitochondria may actually adapt to become more efficient at making ATP, reducing an individual’s total energy requirements to perform the same tasks. This adaptation results in the body burning less calories, again favoring weight regain after weight loss.

In extreme weight loss regimes there is typically severe calorie restriction. Because less food is consumed to stimulate weight loss, the gut has to do less work to digest food, therefore lowering the thermic effect of food. With less calories used to digest food, the body is again reducing its total daily energy expenditure, favoring weight regain.

It appears there are many internal factors that adapt during weight loss. This supports the theory that the body has a certain body weight set point that we have little control over.  The question then becomes: “What do we have control over?” 

As individuals:

• We have control over addressing weight loss in a realistic manner, promoting steady gradual weight loss versus extreme caloric restriction and fad dieting to lose weight.
• We have control over that information we choose to take as truth and implement in our daily lives.
• We have control over our home environment and what situations we choose to put ourselves in.
• We have control over our physical activity schedule and the tools we use to manage stress level.
• We have control over our sleep habits and sleep routine.
• We have control over our treat allowance, and our mindful presence in enjoying treat foods – allowing them in as an occasional indulgence versus an impulsive decision.
• We have control over the types of people that we spend time with – who in turn form our social support network.
• We have control over monitoring our own progress, setting small goals that are measurable and realistic. If you stuff a whole apple in your mouth at once you will choke. Take one bite at a time and savour the apple.

If implemented consistently, research shows that sustained weight loss over 3 years is associated with the following 3 specific behaviors:

• Frequent self-monitoring (food/activity journal)
• Planning meals in advance
• Monitoring of body composition (monitoring weight, body composition analysis or measuring inches)

In summary, extreme weight loss and extreme calorie restriction will lead to extreme metabolic adaptation that persists for years, lowering basal metabolic rate thereby preventing successful long-term weight loss. The slow and steady approach will win each battle and win the overall war for achieving long term sustained weight loss.