An Overview of Reducing Body Fat

Reducing body fat is one of the primary goals for athletes, active adults, and individuals who want to lose weight. Having optimal body composition is shown to improve health, athletic performance, and aesthetic appearance.

According to research, having lower levels of body fat while maintaining lean muscle provides a competitive edge. Other studies indicate that achieving ideal body fat composition is unique based on one's individual energy expenditure.

This means that what works for one active individual may not be the best weight management approach for another.

Common questions surrounding fat loss can include:

  • Why does body fat seem to store mostly in one area?
  • Is spot reduction a valid method for fat loss?
  • Does the fat burning zone really exist in exercise?
  • Is diet or increased exercise the best way to lose fat?
  • Can I increase fat loss by consuming certain foods or supplements?

    When it comes to reducing body fat for the active adult or athlete, many factors need to be considered. According to a review published in the Journal of Sports Medicine, weight loss needs to be implemented in a balanced way to preserve lean muscle. In order to achieve this goal, it’s important to have a full understanding of how fat works in our body before starting the process of reduction.

    Fat Burning Basics

    Fat reduction is difficult for most individuals—exemplified by more than 66 percent of the United States population being overweight or obese. Although active adults and athletes typically don’t fall into this category, they do struggle with body weight issues specific to their sport.

    Whether weight loss is for health improvement or enhanced athletic performance, reducing fat is the goal in both cases. Generally, active individuals or athletes wanting to lose weight fall into two categories:

    1. Overfat or obese according to body fat levels
    2. Already lean but desire additional body fat reduction (athletes participating in weight-sensitive sports)

    Reducing body fat and achieving successful weight management requires an individual to understand energy balance. Energy balance means the number of calories consumed equals the number of calories expended (burned). Calories are units of energy from food which the body uses for normal functioning and physical activity. A simple formula to easily understand energy balance over time is:

    • Energy (calories) in is the same as energy burned = weight stays the same
    • Energy in is more than energy burned = weight gain
    • Energy in is less than energy burned = weight loss

    Energy balance is a dynamic process, according to research. When a goal to lose or gain weight is implemented, a change in the formula will occur.

    For example, changing energy input will affect the other side of the equation—energy output—and the achievement of specific results.

    According to the Journal of Sports Medicine, factors influencing either side of the energy balance equation include:

    • Total energy expenditure (calories burned)
    • Total energy intake (calories consumed)
    • Dietary macronutrient composition (total percent ratio of carbs/proteins/fats)
    • Energy density of the diet (carbohydrates/fats)
    • Altered thermic (metabolized) effect of food depending on dietary nutrient breakdown
    • Energy type being used during exercise (carbs or fats)
    • Exercise type, intensity, and duration 
    • Non-sport related activities (walking, biking, yoga)
    • Sedentary lifestyle when not training

    Food and Fat Loss

    The body uses carbohydrates and fats as primary and secondary energy sources. The primary role of protein is not so much for energy but to build and repair muscle tissue. Carbohydrates, fats, and protein are all macronutrients essential for health and optimal fitness.

    Balancing these nutrients according to energy output is vital for reducing body fat. Each macronutrient releases a different amount of energy into the body when consumed:

    • Carbohydrates: four calories per gram
    • Protein: four calories per gram
    • Fats: nine calories per gram

    Food provides energy at varying rates per macronutrient as outlined above. Knowing fat contains nine calories per gram may lead you to believe eating less fat is the best strategy to lose fat for example. This is far from the truth.

    Active adults and athletes depend on calories from all macronutrients to reduce body fat and preserve lean mass. Total caloric (energy) intake compared to caloric output ultimately determines if we are overweight, obese, or in energy balance.

    Furthermore, active adults and athletes will often have higher levels of body fat when not competing. This is due to being more relaxed about their diet while off-season. However, this causes many athletes to restrict calories when preparing for their sport and looking to reach competitive weights.

    Caloric restriction is shown to have adverse health effects for athletes and is not the best method for body fat reduction.

    Research indicates that the ultimate goal for an athlete is to achieve a healthy body weight year round, minimizing the need to extreme diet for competition. According to the International Journal of Sports Nutrition and Exercise Metabolism, athletes are advised to lose weight gradually at a weekly rate of 0.7 percent (slow reduction).

    In order to achieve healthy body weight and healthy body fat levels, the Journal of Sports Medicine suggests that one considers the following:

    • Does my goal weight promote good health and eating habits?
    • Does my goal weight increase the risk of injuries?
    • Does my goal weight support healthy age-related body development, including normal reproductive function?
    • Can my goal weight be maintained without chronic dieting or caloric restriction—which could lead to disordered eating behaviors?

    Cutting Fat With Exercise

    According to the Journal of the International Society of Sports Nutrition, body fat is reduced by adjusting caloric intake to individual energy expenditure (exercise). Therefore, cutting fat is a dynamic process involving both energy input and output.

    Research indicates that the body also experiences thermogenic adaption as weight is reduced. Thermogenic adaption refers to a metabolic process of how the body burns energy. The burning (thermic) effect can be significantly impaired by weight loss. How much energy is burned in the form of fat is different for each individual and depends on:

    • Basal metabolic rate (BMR/resting energy expenditure)
    • Exercise activity thermogenesis (EAT)
    • Non-exercise activity thermogenesis (NEAT)
    • Thermic effect of food (TEF)

    Weight loss decreases the function of all the above categories in athletes and active adults, according to research. It is recommended that athletes watch for signs of weight loss plateau and implement energy intake or expenditure adjustments to favor continued body fat reduction.

    Also suggested is participation in a resistance training program with adequate protein intake to promote muscle growth. Higher protein diets are shown to decrease adaptive thermogenesis, stimulate fat burning, and promote satiety.

    Energy intake and output determine fat loss and our energy systems play an important role in this process. Depending on the exercise, specific and different energy systems are used to support the workout. That means our body is working either aerobically (with oxygen) or anaerobically (without oxygen).

    We also burn carbohydrates (sugar), fats, or stored chemicals during activity. The following energy systems are used by the body during specific exercise: 

    • Phosphagen system: Used during short-term, intense activities lasting five to 15 seconds (weight lifting and sprints). The body uses creatine phosphate and adenosine triphosphate (ATP) stored in our muscle for a quick energy source. Because the body doesn’t require oxygen to drive this system, it’s considered anaerobic.
    • Glycolysis system: Primary energy system for intense exercise lasting 30 seconds to two minutes (interval training or HIIT workouts). Energy is supplied through carbohydrates converted into blood glucose (sugar) or muscle glycogen (stored form of glucose). This system is typically anaerobic as oxygen is not supplied fast enough to meet the needs of the muscle.
    • Aerobic system: Used during long duration, low-intensity exercise (walking, jogging, endurance running). The body uses the stored form of carbohydrates (blood glucose) or fats as fuel to power the physical activity. The aerobic system depends on oxygen and is considered the most complex of the energy systems.

    Varying training methods to challenge the different energy systems is a great way to reduce body fat. Energy output or calories burned during a workout is directly related to exercise type, intensity, and duration of the program.

    Consistent exercise using varying energy systems is shown to promote increased oxygen function and help our cells burn fat more efficiently too. Also, circulation increases—improving fatty acid availability as an energy source during physical activity.

    Metabolism and Cutting Fat

    Metabolism can be described as many internal processes working together to create the energy our body needs for life and optimal fitness. According to research, energy (caloric) restriction and weight loss can impair our metabolism and, therefore, our energy expenditure.

    Other studies show a decrease in exercise activity thermogenesis (EAT) in response to weight loss. This means our body is unable to burn calories efficiently during exercise. 

    According to the Journal of the International Society of Sports Nutrition, caloric restriction and weight loss result in a reduction of metabolically active tissue. Decreased metabolic tissue also lowers our basil metabolic rate (BMR)—the ability to burn calories in a non-exercise state or at rest.

    Other research suggests that when energy input is too severe the body goes into adaptive thermogenesis. Adaptive thermogenesis occurs as a “function to promote the restoration of baseline body weight.” Metabolic dysfunction and adaptive thermogenesis explain why weight loss plateaus occur regardless of reduced caloric intake.

    In order to avoid metabolic dysfunction and adaptive thermogenesis, it is recommended that athletes and active adults implement a slow approach to fat loss. Research suggests using small energy deficits and monitoring progress to achieve the goal of continued healthy fat reduction.

    Hormones and Fat Loss

    Hormones play a vital role in energy intake, energy output, and overall body composition. Research indicates that:

    • Hormones of the thyroid gland help regulate metabolism.
    • Leptin hormone—made in fat cells—regulates energy availability and expenditure.
    • Insulin and cortisol hormone—released from our adrenal glands—assists metabolic function.

    According to studies, unfavorable changes to these circulating hormones occur in response to caloric restriction or low body fat. The body will protect itself through a “homeostatic endocrine response aimed at conserving energy and promoting energy intake.” Simply stated, our hormones will work to bring the body back into balance, hold onto energy stores, and stimulate a hunger response so we will eat more.

    Maintaining balanced hormone function is vital while cutting fat. It is recommended athletes and active adults use appropriate methods of weight loss. According to research, small adjustments to energy intake work best for optimal body functioning and reaching desired body composition.

    Unsafe Methods to Reduce Fat

    Athletes and active adults often feel pressure to achieve ideal body composition for their sport. This issue has caused many athletes to resort to unsafe methods of weight loss. Voluntary dehydration, caloric restriction, and disordered eating are common unsafe weight loss practices among athletes.

    In order to minimize unsafe weight loss methods, the National Athletic Trainers' Association has provided guidelines to safely reduce body fat. However, rapid and unsafe weight loss methods are still common among athletes in the following sports:

    • Boxing
    • Wrestling
    • Martial arts
    • Football
    • Dance
    • Distance running
    • Cycling
    • Bodybuilding
    • Gymnastics

    Ideal Body Fat Levels

    Achieving an ideal body fat level is unique to each individual. It also varies among athletes, active adults, and those who just want to reduce fat. One of the most referenced and commonly used body fat percent charts is provided by the American Council on Exercise (ACE):

    DescriptionWomenMen
    Essential fat10-13%2-5%
    Athletes14–20%6–13%
    Fitness21–24%14–17%
    Average25–31%18–24%
    Obese32%+25%+

    A Word From Verywell

    Reducing body fat is a dynamic process for athletes, active adults, or even newbies wanting to lose weight. It will be important to implement proper nutritional and exercise practices to ensure safe and healthy weight loss.

    The goal of achieving an ideal body composition also includes learning the best balance of energy intake and output for you. Taking it slow will ensure your body continues to run efficiently to support your workouts while achieving desired results.

    Sources

    Eric T Trexler et al., Metabolic adaptation to weight loss: implications for the athlete, Journal of the International Society of Sports Nutrition, 2014

    Garthe I et al., Effect of two different weight-loss rates on body composition and strength and power-related performance in elite athletes, abstract, International Journal of Sports Nutrition and Exercise Metabolism, 2011

    Healthy Weight Basics, Balance Food and Activity, National Institutes of Health, 2013

    Melinda M. Manore, Weight Management for Athletes and Active Individuals: A Brief Review, Sports Medicine, 2015

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