On the face of it weight loss is a simple enough equation – expend more energy than you consume from food to achieve so called ‘negative energy balance’. Just eat less, exercise more and the resulting energy deficit will force your body to ‘burn’ fat. Cue restrictive diet and endless hours on the elliptical trainer in the gym. Of course eating less and doing some exercise is a great start, but weight control turns out to be a little more complex, which may explain why so many of people find their initial enthusiasm for a weight loss programme quickly tempered by the reality of slow or non-existent weight loss.
The American Society for Nutrition recently assembled a meeting of experts in the field of obesity to better understand the limitations of the energy balance model. Perhaps the most striking part of their subsequent report (1), is how the conventional method for calculating the potential rate of weight loss through calorie restriction grossly overestimates what is possible.
Conventional wisdom suggests that cutting food intake by 500 calories per day (3500 calories per week) equates to weight loss of approximately 0.5-1Kg (1-2lbs) per week. Yet a model based on recent research finds the rate is much lower. For example, the old calculations suggest it will take a mere five to ten weeks to lose 5Kg based on a 500 calorie per day restriction, whereas the new model estimates it taking over six months – assuming 100% compliance with the diet. Significant weight loss necessary for obese individuals to reach a healthy weight will take several years. No wonder so many weight loss regimes end with disillusionment, disappointment and failure – in short, unrealistic expectations.
Accurate estimations of weight loss based on calorie restriction can be found at www.pbrc.edu/the-research/tools/weight-loss-predictor and a more complex version taking account of exercise changes at http://bwsimulator.niddk.nih.gov.
Energy balance is only one part of the story though and the contribution of other factors and their interactions need to be addressed if weight loss efforts are to be ultimately successful.
Essentially, this describes how your body maintains physiological balance. Homeostatic mechanisms control essential systems like body temperature, breathing rate, heart rate blood pressure and so on. Homeostatic mechanisms also exist to maintain even weight in the face of fluctuating energy intake. In other words decreasing your food intake triggers regulatory processes designed to maintain weight. For example levels of the hormone grehlin rise with time since you last ate. Grehlin stimulates appetite, making you feel hungry. Another hormone, leptin, is an appetite suppressor and promotes fat burning, with levels rising during and after eating. Leptin is secreted by fat cells so as fat begins to accumulate leptin levels rise to suppress appetite and promote fat burning, thereby regulating weight back to normal. Why then, you might ask, do we get fat in the first place if these processes are so effective? It appears that the modern high fat, highly refined diet combined with certain lifestyle factors disrupt or override these balancing mechanisms.
Elevated blood glucose levels, high cholesterol, elevated blood pressure and fat accumulation around the abdomen are collective called ‘the metabolic syndrome’. The underlying problem is one of hormone imbalance, specifically insulin, the hormone that transports sugars from the blood into cells to be used for energy. Consumption of highly refined carbohydrates such as processed food, fast food, white bread, cakes, biscuits and confectionary trigger insulin release. In time cells become resistant to insulin’s effects resulting in both high levels of insulin and sugar in the blood. As insulin is an anabolic hormone it promotes the storage of excess energy as fat, particularly around the abdomen and internal organs leading to weight gain. In addition excess sugar in the blood is linked with increased cardiovascular disease risk.
Metabolic syndrome therefore highlights one of the key limitations of the energy balance model, which considers all calories equally no matter what their source. Where 100 calories from a sugary soft drink are counted the same as 100 calories from wholemeal bread despite their very different effects on physiology. Recent studies show that following a diet that emphasises low glycaemic index foods such as wholemeal bread, whole grains, brown rice, beans, legumes, vegetables and includes adequate lean protein and fibre is most effective for promoting sustainable weight loss (2).
Obese people tend to have high levels of the hormone leptin, which under normal circumstances is an appetite suppressant. In obesity though, the brain becomes indifferent to leptin’s usual effects and the normal feedback of feeling full when eating is effectively switched off. This is called leptin resistance and explains why when leptin drugs were developed to combat obesity they did not work. Eating refined carbohydrates, sugars and especially high fructose corn syrup (as used in many soft drinks) contributes to leptin resistance. Other factors include lack of sleep and cellular toxicity.
It is estimated that around eighty thousand new chemicals have been introduced into the environment in the last hundred years or so. Industrial activities, intensive farming methods, household and personal care products, cigarette smoke, plastics, tetraethyl lead hanging around in the atmosphere from the old leaded petrol days, the list goes on and on. Environmental toxins appear to affect thyroid function, and therefore metabolic rate, as well as triggering inflammation and disrupting hormonal controls of appetite and fat burning, including leptin. To make matters worse many toxins are stored in fat tissue, so the more overweight you are, the more toxic you are likely to be. In fact there is evidence that the release of toxins from fat stores during weight loss may actually inhibit further weight loss, providing another possible reason why hitting a weight loss plateau is so common (3).
Recent research conducted in the USA found that American adults sleep 1-1.5 hours less than their counterparts in the 1960s and that since then those sleeping less than 7-hours has increased from 15.6 to 37.1% (4). One theory is that the advent of the internet, 24-hour TV, email, longer working hours, longer commuting times and more evening and weekend work has resulted in more sedentary behaviour. In addition, more time awake means more opportunities to eat, and with increasingly busy lifestyles, poor food choices are more likely. It is also possible that sleep deprivation and poor sleep patterns disrupt our old friend leptin, further increasing the likelihood of weight gain (4).
Stress hormones disrupt blood glucose levels exacerbating insulin resistance and metabolic syndrome symptoms (5). Stressed people tend to eat more refined and sugary foods, smoke more and drink more, increasing toxin exposure. And of course stress can disrupt sleep quality and duration. In short, if you are stressed you are making weight loss even harder than it already is.
The Bottom Line
For sustainable weight loss calorie restriction of only 250-500 calories less than normal weight maintenance intake is sufficient, but needs to be sustained consistently for many months, if not years. Opt for low GI carbohydrates such as wholemeal bread, whole grain cereals, brown rice, beans, legumes and vegetables with adequate protein from lean meat, fish, eggs, nuts, seeds and legumes. A varied diet that includes fresh fruit and vegetables, nuts and seeds provides vitamins, minerals a myriad of plant compounds that support detoxification, hormone regulation, inflammation control and energy metabolism. Ultimately weight control is not about ‘doing a diet’ for a few weeks, it is about a lifestyle that provides balanced eating with adequate physical activity and sufficient rest. It is time to move beyond calories!
1. Hall KD et al. (2012). Energy balance and its components: implications for body weight regulation. Am J Clin Nutr. 95(4):989-94.
2. Thomas DE et al. (2007). Low glycaemic index or low glycaemic load diets for overweight and obesity. Cochrane Database Syst Rev. (3):CD005105.
3. Hyman M (2007). Systems biology, toxins, obesity, and functional medicine. Altern Ther Health Med. 13(2):S134-9.
4. Chaput JP et al. (2008). The association between sleep duration and weight gain in adults: a 6-year prospective study from the Quebec Family Study. Sleep. 31(4):517-23.
5. Nieuwenhuizen AG & Rutters F (2008). The hypothalamic-pituitary-adrenal-axis in the regulation of energy balance. Physiol Behav. 94(2):169-77.