By Tayla Clegg (Athlete
& Student Dietitian, SCU) &
Samantha Staines (ADP)
The term “Your body is a machine” is thrown around a lot when it comes to fueling your body. However, our bodies are in fact very far from a machine. Our bodies are highly complex and adaptive to our behaviours and environment, and this is particularly evident when we talk about energy balance, metabolism and dieting.
What is energy balance?
Energy balance is the relationship between energy intake, energy expenditure, and energy storage. The energy we take in is from the calories in our food and drink, whilst the energy we expend is used by the body for our daily energy requirements. In theory, if there is less energy expenditure than energy intake, this results in a positive energy balance, and generally a gain in weight. Alternatively, a negative energy balance occurs when energy expenditure exceeds energy intake, this is termed a negative energy balance, and generally leads to weight loss. Lastly, when eating the same amount of energy that your body requires, leading to the maintenance of body weight (1).
What are the impacts of dieting on metabolism?
As mentioned, a diet that achieves a negative energy balance, or “calorie deficit”, is necessary for weight loss. However, with this deficit, we also see metabolic and hormonal adaptations occur, that can may slow down weight loss or impact our capacity to reach certain weight loss goals. This is because our body has functions that aim to help us survive, and from an evolutionary perspective, losing weight is not beneficial to survival.
These adaptations as we mentioned, come from different systems of the body, including hormonal and metabolic processes, that play role a in regulating body composition, energy intake, and expenditure. Some of these impacts include:
1. Reduction in BMR
Your basal metabolic rate (BMR) or resting metabolic rate (RMR) is inclusive of components such as sleep, training status, energy availability, nutrient balance, and body composition. During dieting, we see a reduction in muscle mass/metabolically active tissue as weight is lost, and this reduction results in a reduced BMR. To complement this statement, a study has shown that highly trained athletes, who have high energy intake and energy turnover, tend to have increased BMR, as a result of their training status and maintenance of lean body mass (2). This is why preserving muscle mass during a period of dieting is key to sustained weight loss. Including some form of resistance training a few days a week and including good sources of protein at regular intervals (20g every 3-4 hours) is key to maintain muscle mass, and thus promoting maintenance of our basal metabolic rate.
2. Reduced energy availability
Being in a deficit for an extended period means your body starts to reduce energy availability. Individuals dieting tend to lack energy, generally, we feel worse, unable to recover as well, and do everything the body needs to. If energy availability is low enough, the body may begin to shut down or reduce all non-essential uses of energy, which explains why women can lose their menstrual cycle (3), which is a complex issue that should be raised with your dietitian or health care team.
3. Reduction in NEAT
NEAT stands for ‘non-exercise thermogenesis’. It consists of the movement-based patterns we participate in, that aren’t regimented into our day, such as fidgeting, standing at work, or carrying the groceries. Studies have demonstrated that NEAT increases with weight gain/increased energy intake and decreases with weight loss/decreased energy intake, based on lower movement (4).
4. Reduction in TEF
TEF is the ‘Thermic Effect of Food’ and is defined as the increase in metabolic rate after ingestion of a meal (5). With reference to dieting, a study has suggested that as meal size increases, we see an increase in TEF post-meal ingestion, which explains why skipping meals is not ideal for weight loss. Additionally, feelings of fullness and satiation are also linked with TEF, and it is known that meals that are high in protein are the most thermogenic and satiating, which is highly beneficial for sustainable weight loss (6).
How to lose weight safely and sustainably?
The way an individual goes dieting is incredibly important, in order to enable the body to function efficiently and effectively (7). Careful planning around diet and exercise is necessary for safe sustainable weight loss. Some helpful tips and approaches that can be used for sustainable weight loss include:
Use filling, nutrient-dense but low energy, foods (e.g. salad, berries, soup) to bulk up your meals and snacks
Include protein at meals and snacks to help manage appetite and reduce muscle loss
Limit high energy foods (e.g. soft drink, chocolate, take-away, desserts, alcohol, etc
Be aware of non-hungry eating (e.g. boredom, procrastination…)
Be patient and persistent! Results don’t happen overnight
Be wary of fad diets or diets that eliminate whole food groups, successful weight loss (and maintenance) requires long term/sustainable approaches
Fuel & recover appropriately around training sessions to avoid impacting the quality or adaptations from sessions
Include resistance training into your exercise routine to build and maintain muscle mass during weight loss, to maintain your BMR
Hydration with a focus on regular water intake
When in an energy deficit for long periods of time and seeing a plateau in weight loss, consider taking a ‘diet break’ or reconsider your nutrition goals
Ensure dieting is done in a safe environment, and it could be a good idea to seek out help from an accredited practicing dietitian