Part 2: Weight Loss Strategy - Increase energy expenditure

Overview

If we want to create an energy deficit for weight loss, increasing energy expenditure can be a helpful strategy. By raising total energy expenditure, we can better support and sustain that deficit over time. However, there are many myths about how lifestyle changes influence the amount of energy we burn. The body primarily expends energy in three ways, and understanding the effectiveness of each is key.

Can We Increase Diet-Induced Thermogenesis?

Diet-induced thermogenesis (DIT) refers to the energy the body uses to digest, absorb, and process the food we eat. It is often suggested that manipulating certain dietary factors such as meal size, macronutrient composition, or eating frequency, can increase DIT and therefore increase total energy expenditure to support weight loss. Several dietary strategies are commonly discussed in relation to increasing DIT.

For example:

• Higher-energy meals increase DIT. Larger meals require more energy for digestion and metabolism. However, increasing the energy content of a meal also increases total energy intake, which counteracts the goal of creating an energy deficit for weight loss.¹

• Macronutrient composition influences DIT. Protein and carbohydrate generally produce a greater thermogenic effect than fat.¹ Because of this, diets higher in protein are often promoted as a strategy to increase daily energy expenditure and support weight loss.

• Meal frequency is often believed to increase metabolism. Some people believe that eating smaller, more frequent meals throughout the day can increase metabolic rate. However, research suggests that meal frequency likely does not significantly influence DIT.²

Although these factors may slightly influence the thermogenic response to meals, the overall impact on total daily energy expenditure appears to be relatively small. Current research also highlights a considerable level of uncertainty regarding how strongly meal characteristics influence DIT.¹

In practice, this means that while DIT does contribute to total energy expenditure, manipulating diet specifically to increase DIT is unlikely to have a large effect on overall energy balance and weight loss.

Can We Increase Basal Metabolic Rate?

Current research shows that a person’s basal metabolic rate is largely determined by non-modifiable factors such as age, sex, genetics, and body composition. This means it is not something that can be significantly altered to make weight loss easier.

In fact, when the body enters an energy deficit, it often responds by reducing basal metabolic rate. This reduction is a survival mechanism designed to conserve energy during periods of limited food availability. As a result, the body may burn fewer calories than predicted.³

This adaptive response means that sustained weight loss may require a greater or more prolonged energy deficit than initially expected. Overall, attempting to directly modify basal metabolic rate is unlikely to have a meaningful impact on weight management.

Strategy: Increasing Physical Activity

The previous two components of energy expenditure, diet-induced thermogenesis and basal metabolic rate, are unlikely to be significantly altered to meaningfully support weight loss. However, physical activity is modifiable, making it the most practical component of energy expenditure to target.

Increasing everyday movement can play an important role in raising total daily energy expenditure. Activities such as walking more, taking the stairs, standing more often, performing household tasks, or moving regularly during work can all contribute to increased energy use throughout the day. This type of movement is often referred to as incidental physical activity.

Although each individual movement may burn only a small amount of energy, these activities accumulate over the course of the day and can meaningfully contribute to the energy deficit required for weight loss. There are no clear guidelines for how much incidental physical activity a person should aim for or how best to measure it. Instead, a practical approach is simply to increase movement whenever possible throughout the day.

Structured exercise can also support weight loss and provide many additional health benefits, including improvements in cardiovascular fitness, strength, mood, and metabolic health. It is a common belief that exercise is crucial for weight loss. However, relying on exercise alone as a primary strategy for weight loss is often unrealistic and without appropriate knowledge a hindrance.

How much exercise is needed to lose weight?

We can estimate how much energy a person expends during exercise and use this to approximate how much activity might be required to produce an energy deficit.

Hypothetical example (Walking):

A 100 kg male who is currently in energy balance wants to lose 1 kg of body fat using exercise alone. To achieve this, he would need to create an energy deficit of approximately 7,700 calories, which is roughly equivalent to the energy stored in 1 kg of body fat.

If this person chooses brisk walking as their primary form of exercise, we can estimate the energy expenditure. A 100 kg male brisk walking at approximately 5.5 km/h expends roughly 4.7 calories per minute from the activity itself (excluding their current resting metabolic rate).

To create a 7,700 calorie deficit through walking alone in one week, this person would need to walk:

• 27.5 hours (~3.9 hours per day)

• Roughly 151 km

For most people, this amount of walking is clearly unrealistic to sustain.

You might assume the solution is to simply increase the intensity of exercise. However, this introduces another limitation: a person’s fitness level must be able to tolerate higher-intensity activity for a prolonged period.

Hypothetical Example (Running)

If the same 100 kg male were to run at approximately 10 km/h, he would still need to run for about:

• 8.5 hours per week

• Roughly 85 km per week

For someone who is new to exercise, completing this volume of running at that speed would be extremely difficult and may also increase the risk of fatigue or injury.

Considerations with exercise and weight loss

There are several additional factors that can make relying on exercise alone for weight loss challenging:

• Reduced incidental activity: Research suggests that when people begin exercising, they may unconsciously reduce their incidental physical activity throughout the rest of the day. As a result, the increase in exercise energy expenditure from exercise may be partially offset by a decrease in incidental activity.⁴

• Increased hunger and appetite: Exercise can increase hunger in some individuals, which may lead to increased energy intake and reduce the overall energy deficit.⁴

• Improved exercise economy: As a person becomes fitter, their body becomes more efficient at performing the same activity. This means that the same exercise session may burn fewer calories over time as the body adapts.⁴

• Time constrains: The amount of exercise required to produce a large energy deficit can be time-consuming and difficult to maintain long term. Many people have other commitments such as work, family, daily tasks that can cause daily exercise challenging for people.

Is exercise important?

Exercise plays a crucial role in improving overall health and wellbeing. Research consistently shows that a person’s cardiorespiratory fitness level is one of the strongest predictors of all-cause mortality, meaning that individuals with higher fitness levels generally have a lower risk of death from various causes. It also reduces the risk of many diseases and disorders and helps keep people stronger, fitter and more mobile.^4,5

When it comes to weight loss, exercise tends to play more of a supportive role alongside dietary interventions. While exercise alone may not produce large energy deficits for most people, it can still play an important role in weight loss by increasing total daily energy expenditure.

For these reasons, exercise should be viewed not only as a tool for weight management, but as one of the most important behaviours for improving long-term health.

Reference

1. Quatela A, Callister R, Patterson A, MacDonald-Wicks L. The Energy Content and Composition of Meals Consumed after an Overnight Fast and Their Effects on Diet Induced Thermogenesis: A Systematic Review, Meta-Analyses and Meta-Regressions. Nutrients. 2016 Oct 25;8(11):670. doi: 10.3390/nu8110670. PMID: 27792142; PMCID: PMC5133058.

2. Taylor MA, Garrow JS. Compared with nibbling, neither gorging nor a morning fast affect short-term energy balance in obese patients in a chamber calorimeter. Int J Obes Relat Metab Disord. 2001 Apr;25(4):519-28. doi: 10.1038/sj.ijo.0801572. PMID: 11319656.

3. Dulloo AG, Jacquet J. Adaptive reduction in basal metabolic rate in response to food deprivation in humans: a role for feedback signals from fat stores. Am J Clin Nutr. 1998 Sep;68(3):599-606. doi: 10.1093/ajcn/68.3.599. PMID: 9734736.

4. Byrne NM, Hills AP. How much exercise should be promoted to raise total daily energy expenditure and improve health? Obes Rev. 2018 Dec;19 Suppl 1:14-23. doi: 10.1111/obr.12788. PMID: 30511509.

5. O'Keefe JH, O'Keefe EL, Eckert R, Lavie CJ. Training Strategies to Optimize Cardiovascular Durability and Life Expectancy. Mo Med. 2023 Mar-Apr;120(2):155-162. PMID: 37091937; PMCID: PMC10121111.