You will notice that headline said: “Why Can’t Fat People Lose Weight?” rather than: “Why Fat People Can’t Lose Weight”. The second headline implies that it’s all over and if you’re fat you have no hope of slimming down — permanently. But that’s not the question because fat people definitely can lose weight. It happens all the time when people get sick and die. It’s called the First Law of Thermodynamics. And no, this is not some abstruse and irrelevant pun, it’s at the very core of how weight control needs to be approached.
What we don’t need is a new distraction based around a new nonsense like ‘leptin resistance’ (and see below) that gives people an excuse not to control their energy intake and expenditure. Insulin was once the big bad hormone, and now leptin is showing signs of being the new insulin.
With the obesity epidemic in full swing, and the incidence of obesity and diabetes (and other associated diseases) set to mushroom in the next decades, it seems professionals are rushing to provide explanations for why this obesity pandemic is out of control in developed countries and soon to follow in emerging super states like China and India as affluence blooms. Obesity in the 2000s is very much a product of the inevitable relaxation of environmental and social constraints that come with affluence — and by affluence I mean cheap food, abundant availability and less physical activity — in work, leisure, travel or transport.
The New Hormones
There are no new human hormones of course, only new ones to focus on. Insulin was a focus in the most recent decade, when diet books and fitness protocols tried to tell us it was all about insulin and if you controlled it you would not get fat and could look like Mr Universe. This was always a half-truth. Now it’s a new tray of hormones — the ones that pop up or down when the body senses it needs to feed or stop feeding — the appetite and satiety hormones.
Exercise and diet (calorie restriction) are the mainstream recommendations by weight loss professionals when advising clients how to lose weight. Organizations such as the The National Weight Control Registry and WeightWatchers record the fact that this can be a successful approach to fat loss and ongoing weight management for many people.
However, for people who are not successful, an inability to control excessive eating may be a cause of this lack of success. While this may simply be lack of determination and will, or even inadequate information, pundits such as Gary Taubes claim that exercise does not work for weight loss because it stimulates appetite excessively. Others say that certain types of exercise make us hungrier — or even suppress appetite better than other types. What do we really know about exercise and appetite?
The Satiety and Appetite Responses
The human body has a sophisticated system of hormones that affect basic human physiological function. Hormones are essential chemical messengers that cells in the body send out to influence other cells and achieve a particular bodily function. Some of these hormones reflect and react to feeding or fasting. The appetite and satiety hormones, to a certain extent, tell us when to eat (appetite) or when we feel full (satiated). Here are four important satiety and appetite hormones.
- Insulin is produced by the pancreas in response to food intake, especially protein and carbohydrate. At the same time, insulin dampens appetite by sending signals to the brain. In overweight and diabetic people, insulin resistance may cause this regulation to malfunction.
- Leptin is produced by fat cells, increases with body fat levels and is higher in fat and obese people. Leptin is also supposed to dampen appetite in a manner similar to insulin – sending brain signals. However, leptin resistance may also be a factor in wayward appetite in overweight people.
- Ghrelin is released by the empty stomach and its role is to stimulate appetite. Once food is consumed, ghrelin release abates in people with normal metabolism.
- Peptide YY (PYY) is another gut satiety hormone, this time released from the intestines. Its role is to dampen hunger as food is consumed.
Various other appetite hormones have been identified and others are being explored.
Exercise and Appetite
In the weight loss, fitness and bodybuilding industries, promoters of services are looking for an angle: a new supplement, a special exercise or piece of equipment, a radical diet, or even a system of exercising that is supposed to help you lose fat and build muscle in a new way.
One of the approaches is to suggest that a particular type of “metabolic” exercise program will burn off that fat and build muscle while keeping your appetite under control by manipulating one or more of the hormones mentioned above. These training programs tend to disparage cardio and promote high-intensity weight training, circuits and interval training. So what’s the truth about such programs?
Various types, volumes and intensities of exercise have been investigated as to their overall effect on appetite and satiety over the short and longer terms. No consistent result has emerged regarding type of exercise, yet the overall evidence suggests that:
- “A better short-term appetite control has been described in active compared to sedentary men, and an exercise intervention was shown to improve appetite control in previously sedentary individuals.” (Martins).
- Also: “Evidence suggests that chronic exercise training typically causes a partial but incomplete compensation in energy intake perhaps due to beneficial changes in appetite-regulating hormones.” (Stensel).
- And: “These findings suggest that large energy deficits induced by exercise do not lead to acute compensatory responses in appetite . . .” (King).
One point to note is that there are significant differences in how exercise affects appetite and satiety in individuals, and perhaps even gender. Anecdotally, swimming has been suggested to increase appetite greater than other activities. Scant evidence exists for this idea and there is minimal knowledge about specific exercise modalities and appetite and satiety.
Ultimately, exercise is an important part of any weight loss program and does not, by itself, cause compensation and overeating in most regular exercisers. Even so, trainers, dietitians and other weight loss professionals should take care to advise clients not to regard exercise as a licence to binge eat. Rather than a physiological response, this type of overeating seems more a psychological response, and one that can probably be curtailed when the relevant energy quotients of various foods and exercise sessions are explained clearly. In addition, what seems to be useful is a wide-ranging program that includes weights, cardio, and some high-intensity interval work as fitness allows.
- J Nutr Metab. 2011;2011:237932. A review of weight control strategies and their effects on the regulation of hormonal balance. Schwarz NA, Rigby BR, La Bounty P, Shelmadine B, Bowden RG.
- Appetite. 2010 Jun;54(3):492-8. Influence of prolonged treadmill running on appetite, energy intake and circulating concentrations of acylated ghrelin. King JA, Miyashita M, Wasse LK, Stensel
- Ann Nutr Metab. 2010;57 Suppl 2:36-42. Exercise, appetite and appetite-regulating hormones: implications for food intake and weight control. Stensel D.
- Int J Obes (Lond). 2008 Sep;32(9):1337-47. A review of the effects of exercise on appetite regulation: an obesity perspective. Martins C, Morgan L, Truby H.