By: Mustafa Soltanian Fard Jahromi

Also published in Medium: https://medium.com/@mustafasoltanian/exercise-versus-diet-the-best-method-for-weight-management-6e8031d05c96

Exercise was traditionally suggested as one of the best methods of losing and maintaining weight. However, when analysed using scientific methods, it becomes clear that diet rather than exercise should be the main method proposed for weight management. In this report I analyse briefly the impact of exercise and diet on a person’s weight. I conclude that due to availability of high calorie foods and the little amount burnt through exercise, any campaign for weight management should concentrate on a person’s diet.

The Energy Needs of an Adult

The human body runs on chemical energy. The chemical energy that fuels our everyday life and activities is through the adenosine triphosphate or ATP for short and adenosine diphosphate or ADP cycle (see Figure 1). When food is consumed, the body converts the energy contained in the food to be used by the body. The usual manner that the energy contained in food is calculated is by calculating the food’s combustible energy (Food and Agricultural Organization of the United Nations, 2003). The measurement of the energy contained in food after consumption is calculated through a unit of measurement known as Kilocalories or Calories in usual wording. The energy requirement of a person is calculated using their height, weight, and gender.

Figure 1
ATP-ADP Energy Cycle

There are various methods for calculating the energy requirements of a person. Two main factors are taken into consideration when calculating a person’s energy requirements. First is their Basal Metabolic Rate (BMR) or the amount of energy the body needs for its basic functions to be alive. The BMR does not take into consideration other activities such as exercise. The other factor taken into consideration when calculating a person’s energy needs is their daily activities.

For a person to maintain their weight, they should be eating as much energy as they use during the day (Osilla, Safadi & Sharma, 2022). If a person uses more energy than they consume then they will lose weight. If a person eats more energy than they use during the day they will gain weight.

One of the most reliable formulae for calculating a person’s energy needs is by using the Mifflin-St Jeor Equation as follows (Medscape, 2024): 

Females: (10 * weight in kg) + (6.35 * height in cm) — (5 * age in years) — 161
Males: (10 * weight in kg) + (6.35 * height in cm) — (5 * age in years) + 5

To factor in exercise, the Mifflin-St Jeor Equation multiplies by the following numbers:

● Sedentary * 1.2
● Lightly active * 1.375
● Moderately active * 1.55
● Active * 1.725
● Very active * 1.9

Accordingly, a 30 year-old male who is 175 cm tall and weighs around 70 kg with very little or no exercise would need to consume 1,999.5 cal per day to maintain weight. The same male, if he has an active life which could include six to seven intense exercises, three to four times a week, would need to consume 2,874.28 cal per day. About 1000 cal more in the second instance. 

Males: (10 * 70) + (6.35 * 175) — (5 * 30) + 5 = 1,666.25 * 1.2 = 1,999.5 cal (sedentary)
Males: (10 * 70) + (6.35 * 175) — (5 * 30) + 5 = 1,666.25 * 1.725 = 2,874.28 cal (active)

Applying a similar standard for a 30 year-old sedentary female who is 165 cm tall and weighs 60 kg would mean she would need 1,604.1 cal per day to maintain her weight. If she has an active life, she would need 2,305.89 cal per day to maintain her weight, a difference of about 700 cal.

Females: (10 * 60) + (6.35 * 165) — (5 * 30) — 161 = 1,336.75 * 1.2 = 1,604.1 cal (sedentary)
Females: (10 * 60) + (6.35 * 165) — (5 * 30) — 161 = 1,336.75 * 1.725 = 2,305.89 cal (active)

How Much Calories in Common Foods?

The energy contained in natural ingredients can vary between different food items being as low as 15 cal per 100 grams to as much as 607 cal per 100 grams for cashew nuts. Meat items such as a chicken drumstick could contain 239 cal per 100 grams while basic economy beef mince could contain as much as 332 cal. Vegetables and fruits that contain high amounts of water contain the lowest amount of calories. For example, 140 grams of oranges contain 66 calories and 90 grams of raw broccoli contain 90 calories (Bjarnadottir, 2023; Kubala & Arnarson, 2023).

In terms of fast food, the popular Big Mac contains 590 cal (McDonalds, 2024) and KFC’s Big Snack Burger contains 533.8 cal (KFC, 2024). A can of Coca Cola classic with a weight of 330 ml contains 139 cal (The Coca Cola Company, 2024).

How Much Calories Burn in Different Exercises?

Different types of exercise burn different amounts of calories. A person’s weight and height are also a factor for how much calories (or kcals) are burnt in each exercise session. Taking the same average male and female height and the weights given to each used above Figure 2 is a table of how much calories will be burnt during a number of exercise sessions and outdoor activities.

Figure 2
Table of Calories Burnt with Different Exercises

Adding Up the Numbers

A person would have to do more than two hours of weight training or more than an hour of swimming and gardening to burn the energy consumed to burn the calories consumed by having a Big Mac. If a classic Coca Cola can is added then the person would have to run more than an hour continuously. A 30 year old female who is 165 cm tall and weighs 60 kg and has a sedentary lifestyle can only consume two Big Macs and a can of classic Coca Cola to almost reach their maximum daily maintenance. This does not leave much room for healthier food consumption of fruits and vegetables. To have a third Big Mac she would have to do weight training for more than two hours or swim and garden for a little more than an hour. Anything extra would require more exercise.

Exercise has many health benefits both for a person’s physical and mental well-being (World Health Organization, 2024). However, a person has a limited number of hours that can be spent for different daily activities which include work, spending time with family, commuting to work or other places, sleeping, grooming, and so forth. As a result, a person who is not a professional athlete does not have much time to exercise during the day. Hence, exercise alone cannot effectively be used by a person for weight maintenance.

Conclusion

Even though exercise has many health benefits, the main factor for managing weight is diet in the form of the amount of energy consumed by a person in comparison to the amount of energy used by the same person in their daily activities. To properly manage weight, concentration of any health advice or campaign should be on food intake and diet rather than exercise. Benefits of exercise and recommending exercise should be separated from weight management.

References

Bjarnadottir, A. (2023). Broccoli 101: Nutrition Facts and Health Benefits. Healthline. https://www.healthline.com/nutrition/foods/broccoli

Calculator.net. (2024). Calories Burned Calculator. https://www.calculator.net/calories-burned-calculator.html

Food and Agricultural Organization of the United Nations. (2003). Food energy — methods of analysis and conversion factors. https://www.fao.org/4/y5022e/y5022e04.htm

Kubala, J., & Arnarson, A. (2023). Oranges: Nutrients, Benefits, Juice, and More. Healthline. https://www.healthline.com/nutrition/oranges

KFC. (2024). Burger. https://kfc.co.nz/nutrition

McDonalds. (2024). Big Mac. https://www.mcdonalds.com/us/en-us/product/big-mac.html

Medscape. (2024). Mifflin-St Jeor Equation. https://reference.medscape.com/calculator/846/mifflin-st-jeor-equation

Osilla E.V., Safadi A., & Sharma, S. (2022). Calories. StatPearls. https://www.ncbi.nlm.nih.gov/books/NBK499909/

The Coca Cola Company, (2024). How many calories are there in a 330ml can of Coca‑Cola Classic?. https://www.coca-cola.com/hk/en/about-us/faq/how-many-calories-are-there-in-a-330ml-can-of-cocacola-classic

World Health Organization. (2024). Physical activity. https://www.who.int/news-room/fact-sheets/detail/physical-activity