The number one goal of 90% of my clients has been weight loss. Some people are obese and need to lose a substantial amount of weight for health reasons and other people with a healthy BMI just want to get rid of a few pounds to look and feel better (we all want six pack abs). Weight loss depends on how much energy is used to do work (i.e., to move, digest food, think etc.,) relative to how much energy is consumed and stored (caloric intake). Energy is constant so if the energy output (work done) is greater than the energy input (calories consumed) there will be a negative energy balance which forces the body to tap into fat to make up for that deficit. The energy output consists of a person's resting or basal metabolic rate (BMR), which is the total number of calories a person uses while at rest, and a person's active metabolic rate (AMR), which is the total number of calories a person uses if they incorporate movement. If you want to lose fat then you have to create a daily negative caloric balance by limiting your caloric intake or increasing your BMR and AMR or a combination of both.
There are several factors that influence the BMR, AMR and the rate of weight loss. The BMR is influenced by body composition, age, gender, level of stress, body type (or somatotype), hormones and food intake. The AMR is influenced by the activity level. A negative energy balance is created by controlling the caloric intake. All of these need to be carefully balanced in order to achieve your weight loss goal without compromising your health or losing muscle.
The higher the percentage of body fat the quicker the rate of weight loss. I've trained obese people around 40% body fat who could shed up to 3lbs a week by following a rigorous program. However if you are around 15% body fat then the rate of weight loss is exponentially lower. At you'll be extremely lucky to lose 1 pound per week (the typical amount is 0.5lbs/week). Having a higher percentage of muscle also contributes to quicker fat loss but not as much as many people claim. The common misconception is that muscle is 20x more metabolically active than fat and therefore having more muscle raises your BMR accordingly. Recent studies found that 1 pound of muscle burns about 6 calories per day, not 50 calories as is popularly believed. This is still higher than fatty tissue which burns 2 calories per pound per day.
A person's age and gender also influence the rate of weight loss. As you get older your metabolism slows down because your body tends to lose muscle and gain fat which slows down your ability to burn calories. However this can be attenuated by doing regular cardio, strength training and keeping a healthy diet. There is a slight difference between men and women because men have more testosterone which helps to build muscle and so men will have a higher BMR than women on average because they have more muscle.
The level of mental and physical stress affects the rate of fat loss. Cortisol is a hormone released when the body is under stress such as in a fight or flight situation. It serves a biological function of freeing up energy by breaking down fat and muscle tissue during a stressful event so that the body can use it to fight or flee. However, in today's society we do not use that energy to fight or flee and so it gets deposited back into fat around the abdominal region. Prolonged stress can increase the resting level of cortisol making it very hard to burn fat in the abdominal region.
Humans come in three different body types or somatotypes that are genetically determined: ectomorph, mesomorph and endomorph. These body types represent a continuum of body composition and the ability to gain or lose weight (either muscle or fat). Ectomorphs have the least total body mass (made up of fat, muscle and bone). Ectomorphs tend to be tall and skinny and have difficulty gaining weight because they have a fast metabolism. Weight loss for ectomorphs is not an issue but muscle gain is. Mesomorphs have an average total body mass and can change their body composition very easily. Mesomorphs have an intermediate metabolic rate. Endomorphs have the greatest total body mass and tend to put on weight very easily. Endomorphs have the greatest difficulty in burning fat because they have the slowest metabolism.
The BMR is influenced by the levels of thyroid hormones and the catecholamines epinephrine and nor-epinephrine. Thyroid hormones are thermogenic raising body temperature and BMR. People with hypothyroidism (low level of thyroid hormones) have a very slow metabolism, tend to put on fat very easily and have difficulty losing fat. People with hyperthyroidism (high level of thyroid hormones) have a very fast metabolism, tend to be skinny and have difficulties putting on weight. The sympathetic nervous system is responsible for arousal and utilizing energy to be used in times of stress or arousal. The primary hormones that activate the sympathetic nervous system are epinephrine (adrenaline) and nor-epinephrine. Both of these hormones will increase heart rate and force of contraction, increase blood flow to muscles, suppress hunger, and utilize the body to break down fat and glycogen to produce glucose. Most weight loss pills are stimulants that increase the activity of the sympathetic nervous system. Caffeine is often used in over the counter weight loss pills in conjunction with other stimulants because it increases cardiac output, helps the body to utilize fat as a fuel source by increasing epinephrine levels, and suppresses hunger.
Food intake has the greatest effect on basal metabolic rate. The body has to expand energy when digesting and processing food. This is called the thermic effect of food or diet induced thermogensis. The quantity and type of food ingested influences how much energy is required to process the food. Research indicates that proteins are harder to process than fats and so have a much higher thermic effect. Therefore increasing the quantity of protein in your diet will raise your BMR. Foods that are high in fiber such as celery and grapefruit are the hardest to process and have the highest thermic effect. These foods also have what is called a negative caloric balance because they take more energy to digest than the energy they release from digestion.
Increasing the level of physical activity increases the AMR. The more active you are the more calories are needed. The type of activity you engage in as well as the duration and intensity of that activity influences how many extra calories are needed and from what food source these calories come from.
Contrary to popular belief low intensity and long duration cardiovascular activity doesn't burn more fat than shorter duration high intensity cardio. Numerous studies have demonstrated that high intensity interval training (where the heart rate is between 80-90% of its maximum) is more effective for fat loss than low intensity endurance activity because the body has to make up for the oxygen deficit produced during exercise and it burns calories for up to two hours after you stop exercising. This phenomenon is called excess post-exercise oxygen consumption (EPOC). Resistance training is also recommended for fat loss because not only is energy needed during the workout but also after the workout because the body has to repair and build new muscle and this takes energy. Activities with a heavier weight or resistance level and a lower rep number per set are recommended over activities with a light weight and a high rep number per set because lifting heavier weights produces more microtrauma in muscles which is a stimulus for repair and synthesis.
Carbohydrate is the primary source of fuel for the body and it is the only fuel source besides ketones that the brain can use. Whereas fats and proteins must be converted into intermediate forms before they can be used as fuel. Before, during and after higher intensity physical activity the body needs carbohydrates otherwise the blood sugar will get too low and a person will crash, feel nauseous and throw up. Carbohydrates and proteins are needed to build muscle after heavy resistance training. Therefore, when incorporating physical activity into a weight loss program the body will need an adequate supply of proteins and carbohydrates. I found that when incorporating higher intensity cardio and resistance training into a fat loss program a person's diet should be roughly % 35 carbohydrates, % 45 proteins, and % 20 fats and the maximum daily caloric deficit should not exceed 750 calories.
In order to burn fat a person must maintain a proper caloric intake. Exercise itself is not enough if there isn't a sufficient daily caloric deficit. Fatty tissue is a medium the body uses to store energy. One pound of fat stores 3500 calories therefore 3500 calories have to be used in order to burn one pound of fat. In order to burn fat a person must eat fewer calories everyday than they eat regularly to maintain their current weight. If a person eats 500 fewer calories per day then they can lose 1 pound of fat in 7 days. This rate of 1 pound per week is widely acknowledged by health and fitness professionals as a safe and healthy rate of weight loss. Starvation diets (anything above a 1000 caloric deficit) are unhealthy because the body burns more muscle than fat (fat is needed as an energy source when food is scarce) and because the body isn't getting the essential amount of vitamins, minerals, antioxidants and other phytonutrients that keep us healthy.
Now that you have a better idea of the factors involved in metabolism and fat loss you can incorporate some of these into your weight loss program. However a professional weight loss program incorporates many of these factors at the same time and these factors have to be carefully balanced in order to achieve optimum fat loss results without depriving yourself of essential nutrients and losing muscle and strength. I design fat loss programs that are personalized (I take into account your metabolic profile, activity level, and other relevant physical attributes) and comprehensive (I take multiple factors into account attacking fat from every angle).