By Corinne Prainito To lose weight or burn fat you need to create an energy deficit. This can be achieved one of three ways: purely through exercise, purely through diet, or a combination of both. When you restrict calories from your diet its important not to drop below 10 to 20 percent of your Total Daily Energy Expenditure (TDEE). Why? To avoid triggering the starvation response. The starvation response is an evolutionary development in which the body responds to food shortages by slowing down energy expenditure. During starvation the body starts to slowly feed off itself using fat stores, muscles, and internal organs for energy. In this situation, continuing to burn calories at your normal rate would deplete your energy reserves so quickly that youd die soon after your food supply was cut off. By recognizing when food is in short supply and reducing your energy expenditure the starvation response keeps you alive longer. Unfortunately, your body cant tell the difference between low-calorie dieting and famine. So, irrespective of whether you’re on the “Cabbage Diet” or lost at sea surviving on food rations, the following automatic and unavoidable changes - characteristic of the starvation response - will ensue: Decreased resting metabolic rate (RMR)Reduced thyroid hormone activityMuscle tissue breakdownIncreased fluid lossUp-regulation of fat-storing enzymes and hormonesDown-regulation of fat-burning enzymes and hormonesGreatly increased appetite and food obsessionReduced energy and capacity for work, exercise and play Depression, anxiety, mood swings and reduced concentration Lets take a look at these points in more detail and then follow up with some quick tips and links to stay out of starvation mode and lose fat permanently. Decreased Resting Metabolic Rate (RMR)In response to weight loss through dieting, your RMR decreases by more than is attributable to the loss of either body mass or fat-free mass. Severe caloric restrictions can decrease RMR by 45% (McArdle, Katch and Katch, 2001). Your body depresses metabolism to conserve energy making your diet less and less effective (despite not eating much) until eventually your weight loss plateaus. Reduced Thyroid Hormone ActivityThe thyroid gland plays a major role in the regulation of your basal metabolic rate. When your body senses a severe restriction in calories, serum levels of thyroid hormone (T3) are reduced, which in turn depresses the resting metabolic rate. Thyroid hormone reductions are even more pronounced if your intake of carbohydrates is below 200 calories per day (Serog, et al., 1982). Muscle Tissue BreakdownAs a consequence of low calorie dieting, hormones such as epinephrine, glucagon and cortisol break down stored energy (glycogen, muscle, and fat) and look for amino acids to build new cells. Amino acids are the building blocks of protein. Every day, your body uses protein to make new hair, skin, muscle, hormones, and other cells. Your body has no way of storing protein. If you dont eat enough on a daily basis, your hormones will break down muscle tissue to make these new cells. Along with skeletal muscle, lean tissue loss can occur from critical organs, like your heart!!! This is why people on very low calorie diets, often lose clumps of hair, have dry skin, brittle nails, and an emaciated appearance (McArdle, Katch & Katch, 2001; Otis & Goldingay, 2000). As well as creating energy (glucose) and helping to build new cells, breaking down muscle helps conserve energy. Muscle burns more calories at rest than fat, so your body gets rid of it to lower metabolism whilst trying to preserve your fat stores. This is why your fat loss efforts may plateau even though youre eating very little food. To add insult to injury, when you do start to eat healthy amounts of food again, the calories you take in are stored as fat because your metabolic rate remains low as a result of lost muscle mass. Increased Fluid LossDuring the first week of low calorie dieting and any week of starvation, dieters are often encouraged by rapid weight loss that exceeds what is possible through energy restriction. This rapid loss of weight is largely attributed to fluid loss that comes from breaking down glycogen and/or muscle tissue. Glycogen and muscle are stored with three times their weight of water. To lose one kilogram of weight using glycogen or muscle as fuel you only need a deficit of 1000 calories. Thats a loss of 250 grams of glycogen (or muscle) and 750 ml (or 1.6 pints) of water. On the other hand, to lose one kilogram of weight using fat as fuel you require a deficit of 7000 calories! You cant create this kind of deficit in the space of one week without putting yourself in starvation mode. The result? Your percentage of fat loss goes down, while your percentage of muscle, glycogen and fluid loss goes up (Garrow, 1995). Understand that fluid loss is a fairly normal part of any fat loss program, but make sure you allow your calorie deficit to accumulate over a period of weeks. Create a moderate energy deficit using exercise and diet. During the first week, expect that 70% of weight lost will be water. During the second and third week water loss will lessen to approximately 20% of weight lost, while fat loss will increase from 25 to 70%. By the end of the fourth week, fat loss reductions will increase to around 85% of the weight lost, without a further increase in water loss (McArdle, Katch & Katch, 2001). Up-regulation of Fat-Storing Enzymes and HormonesWhen using a low-calorie diet to lose weight the level of fat-storing enzymes and hormones are increased. The chief fat-storing enzyme is called lipoprotein lipase (LPL), which is produced by fat cells to help store calories as fat. The higher your LPL levels, the more efficient you are at storing fat. LPL is partly controlled by reproductive hormones oestrogen in women and testosterone in men. In women, fat cells in the hips, thighs and breasts secrete LPL. In men, LPL is produced by fat cells in the abdominal region. Fat cells in the thighs and buttocks are used for long-term energy storage, while fat cells in the abdominal area release their contents for quick energy. This may partly explain why men can shift their beer belly more readily than women with their saddlebags (Papazian, 1991). LPL makes it easier to regain lost weight. Basically your levels of LPL rise with weight loss; the higher your body fat to begin with, the higher your LPL levels will be. In other words, the more fat you have before weight loss, the more aggressive your body will be in its attempts to regain lost weight. This helps explain why it is easier for a dieter to regain lost weight than it is for someone who has never been overweight to begin with. A final player worthy of note due to its protection of fat stores is insulin. Put simply, as fat cells shrink, they become more sensitive to the action of insulin and as a result do not release their contents as readily (Papazian, 1991). Down-regulation of Fat-Burning Enzymes and HormonesWhen you create an energy deficit that is either too high, or through diet only, your body responds by reducing levels of fat-burning hormones and enzymes. The key is to create a small dietary deficit and exercise! Moderate exercise, 4 to 6 times per week will incite metabolic changes that facilitate fat breakdown. Greatly Increased Appetite and Food ObsessionLow calorie diets fail because they make you hungry. To meet energy needs during times of deprivation your body produces hormones that tell your brain to search for food and eat whatever is available. Your body will crave high-sugar, high fat foods because these foods are very easily digested and therefore best able to meet immediate energy requirements. If deprivation continues cravings will intensify to the point of obsession. Complex carbohydrates and high fiber foods dont feature in food cravings because these foods require too much energy to digest (Otis & Goldingay, 2000). Reduced Energy and Capacity for Work, Exercise and PlayLow calorie dieting leaves you feeling lethargic, tired, and unable to workout. To be successful at fat loss its absolutely critical that youre able to train hard aerobically and with weights. Because very low calorie diets provide inadequate carbohydrates, the glycogen-storage depots in the liver and muscles are rapidly depleted (McArdle, Katch & Katch, 2001). This impairs physical tasks requiring high-intensity aerobic effort (cardio) and/or shorter duration anaerobic power output (weights). Depression, anxiety, mood swings and reduced concentrationDieting affects your mood by messing with neurotransmitters, cell membrane activity and hormones. Serotonin is just one of the neurotransmitters affected by dieting. Its synthesis in the brain is dependent on the supply of an amino acid precursor called tryptophan; even moderate dieting lowers tryptophan enough to reduce brain serotonin levels (Anderson, et al., 1990). Depleted serotonin is linked to depression, anxiety, insomnia, fatigue, low concentration, low self-esteem, over-eating and/or comfort eating. Low fat diets also affect mood because they alter cell membrane activity. Within one-month mood disturbances can be seen when dietary fat is reduced from 41 to 25% of total energy intake. In particular, a reduced intake of omega-3 fatty acids may predispose individuals to depression (Wells, et al., 1998). Neglecting to eat regular meals can also cause problems. People who eat regular meals (starting with breakfast) are calmer, less forgetful, more focused and better thinkers than their meal-skipping counterparts. Skipping meals or eating too few calories stimulates the release of fight or flight hormones, like epinephrine, which can leave you feeling jittery, anxious and irritable. Finally, dieters tend to live on a rollercoaster of emotions. They are more vulnerable than non-dieters to external situations good or bad and often respond by overeating. This happens because dieters are insecure and uncertain about the internal messages their body sends them. To lose weight through dieting alone, internal regulatory cues such as hunger and fullness are ignored and food intake is regulated by some outside force, such as the rules of a chosen diet. Over time ignoring hunger leads to a general lack of internal sensitivity and heightened emotional responses to social or environmental influences (Polivy & Herman, 1995). If you dont have coping mechanisms in place to deal with outside stressors, youll most likely respond by overeating. Lets look at a real life example to get a clearer picture: You (the chronic dieter) have had a good day at work and youre looking forward to coming home and seeing your spouse. You walk through the door greet your spouse warmly, only to receive a half-hearted response. You are devastated and respond by yelling at your spouse for hurting you and being cruel to you with his/her lack luster attitude. Your spouse (a little shocked at this point) responds with a feeble apology and mumbles something about their car breaking down Youve missed their explanation (although at this point you no longer care) because youre already at the local store buying a tub of Ben and Jerrys. When you get home you polish off the whole thing while your spouse cowers in the corner pretending to watch TV. If your spouse is really unlucky youll proceed to blame him/her for making you eat a whole tub of ice cream and blowing your diet. The moral of this weight loss story: Avoid the starvation response by creating a small caloric deficit that never goes below your minimum daily energy requirements (1200-calories for women and 1800-calories for men). Begin your day with breakfast followed by small balanced meals every three hours or so. And ensure youre burning fat not muscle by losing weight gradually no more than to 1 kilogram (1 to 2 pounds) per week. References Anderson, I. M., Parry, B. M., Newsholme, E. A., Fairburn, C. G. and Cowen, P. J. (1990, November). Dieting Reduced Plasma Tryptophan and Alters Brain 5-HT Function in Women. Psychological Medicine, 20(4), 785-791. Abstract retrieved February 25, 2006, from PubMed database site http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=2284387&dopt=Citation. Garrow, J. S. (1995). Effect of Energy Imbalance on Energy Stores and Body Weight. In K. D. Brownell and C. G. Fairburn (Eds). Eating Disorders and Obesity: A Comprehensive Handbook (pp 38 41). New York: Guildford Press. Keys, A., Brozek, J., Henschel, A., Mickelsen, O., and Taylor, H. L. (1950). The Biology of Human Starvation. Minneapolis: University of Minnesota Press. McCardle, W. D., Katch, F. I. and Katch, V. L. (2001). Exercise Physiology: Energy Nutrition and Performance (5th Ed.). Baltimore: Lippincott Williams & Wilkins. Otis, C. L. and Goldingay, R. (2000). The Athletic Womans Survival Guide. United States: Human Kinetics. Papazian, R. (1991). Never Say Diet. Retrieved February 23, 2006, from http://www.fda.gov/bbs/topics/consumer/CON00111.html. Polivy, J. and Herman, P. (1995). Dieting and Its Relation to Eating Disorders. In K. D. Brownell and C. G. Fairburn (Eds). Eating Disorders and Obesity: A Comprehensive Handbook (pp 83 86). New York: Guildford Press. Serog, P., Apfelbaum, M., Autisser, N., Baigts, F., Brigant, L., and Ktorza, A. (1982). Effects of Slimming and Composition of Diets on VO2 and Thyroid Hormones in Healthy Subjects. American Journal of Clinical Nutrition, 35, 24-35. Wells, A., Read, N. Langhorne, J. and Abluwalia, N. (1998). Alterations in Mood After Changing to a Low Fat Diet. British Journal of Nutrition, 79, 23-30. 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