This is an interview with the researcher Katherine Cianflone who is studying the nature of body fat. It is now known that body fat is more than just an energy store; it produces various hormones that have an effect on further weight gain, hunger control and some that have an anti-inflammatory action, so form part of the immune system. Ms Cianflone talks about three different hormones produced by body fat: leptin, adiponectin and acylation stimulating protein (ASP).
Leptin is the hormone produced by body fat that tells us we have had enough to eat. The more body fat we have, the more leptin we produce. Unfortunately what actually happens is that as these leptin levels increase, we actually become resistant to its signals and, just as with insulin and diabetes, over time we develop a resistance to leptin, becoming less and less responsive to this signal telling us we’ve eaten enough. So this is one way that having more body fat makes us get fatter.
Lack of sleep also has an effect on leptin production: it is increasingly prevalent that people do not get enough sleep. In the footmarked study, Dr Van Cauter reports that studies show that in 1960 people in America got an average of 8 – 8.9 hours sleep a night; by 1995 this had dropped to 7 hours and in 2004 it was 6 hours a night or less ((Knutson KL, Spiegel K, Penev P, Van Cauter E. The metabolic consequences of sleep deprivation. Sleep Md Rev 2007 June; 11(3): 163-178. A review of sleep studies on metabolic rate.)). Various studies have found that when deprived of sleep, leptin levels drop by about 18%, and the levels of the hormone signalling hunger, ghrelin, rise by 28% ((Taheri S, Lin L, Austin D, Young T, Mignot E (2004). Short sleep duration is associated with reduced leptin, elevated ghrelin and increased body mass index. PLoS Med 1(3): e62 doi@10.1371/journal. pmed. 0010062. This study used 1,024 volunteers )). So when we are tired, we feel hungrier and hear the signals to stop eating less clearly. Furthermore the food we crave is the high carb, high fat comfort food. Therefore a simple weight loss tip is to get more sleep.
The second hormone under the spotlight is adiponectin and this is released from body fat into the blood stream; its levels are closely related to the amount of body fat in adults. The fatter we are, the less we produce. It has a similar effect on the brain to leptin by signalling when we have eaten enough and it also encourages the body to use its fat stores for energy. All this means that the slimmer we are, the more adiponectin we have, and so the more readily we stop eating and, as a final kick to those already struggling with their weight, the more readily the slim burn their body fat. This is a second way that having more body fat makes us fatter. Another effect adiponectin has on the body is that it has an anti-inflammatory action on the cells lining the walls of the arteries and veins and so is part of the immune system. This explains one reason why the obese are more prone to heart attacks.
Finally Dr Cianflone talks about her speciality, acylation stimulating hormone – ASP. ASP produced by our body fat and by our immune system and levels rise after a meal. It stimulates fat storage by increasing insulin levels ((insulin is the fat storage hormone produced as a result of sugar intake in the diet)) and reducing fat burning for energy – so it is a fat sparing hormone; very useful in times of famine but causing problems in the western world’s food abundance. When we are lean, our fasting plasma ((ie ASP levels are measured following a period with no food – eg in the morning before breakfast)) has no ASP circulating. When we are fat then our fasting plasma does contain ASP in circulation. Furthermore, after a meal, ASP levels rise more quickly when we are carrying too much body fat ((Kalant D, Phélis S, Fielding B A, Frayn K N, Cianflone K, Sniderman A D. Increased postprandial fatty acid trapping in subcutaneous adipose tissue in obese women. Dec 2000, journal of Lipid Research, 41 (12): 1963-1968. A small study on 8 lean women and 8 obese women)). This is a third way that body fat helps us gain weight.
Good news, exercise does help lower ASP levels and also improves insulin sensitivity. The footnoted study was on only 8 untrained young men, but following only 2 weeks of cardiovascular exercise, there was a 25% drop in their fasting ASP. The exercise they performed over this period alternated between 2 hours endurance training at a moderate level with 45 minutes of exercise with comprised alternating 3 mins hard work with 3 minutes easy work ((Schrauwen P, Hesselink MKC, Jain M, Cianflone K. Acylation Stimulating Protein: effect of acute exercise and endurance training. Int Journ of Obesity (2005) 29, 632-638. doi: 10.1038/sj.ijo 0802949 Pub online 4 April 2005)) . This is a shame since it is hard to tell from the study if one programme was more effective than the other.
So yes, having excess body fat leads to having yet more excess body fat. To aid weight loss, it will help to get more sleep and do some exercise.