by James J. Kenney, PhD, FACNDr. Kevin Hall, whose study of 14 participants in the "The Biggest Loser" was widely interpreted as demonstrating that the main reason people who lose a lot of weight have trouble keeping it off is they experience a large drop in metabolic rate. This reviewer was rather critical of Dr. Hall's "Biggest Loser" study and especially the media's take on its implications here:  [https://www.pritikin.com/resting-metabolic-rate-healthy-weight-loss]. Although to be fair to Dr. Hall, he did note: "Contrary to expectations, the degree of metabolic adaptation at the end of the competition was not associated with weight regain." The main reason that people on calorie-restricted diets appear to have difficulty losing weight and keeping it off seems to have little to do with abnormally-low metabolic rates but rather gross under-reporting of calorie intake [http://www.nejm.org/doi/full/10.1056/NEJM199212313272701#t=articleTop]. If a slower metabolic rate was responsible for weight loss plateaus and the cause of weight regain, then Dr. Hall would have found a significant correlation between slowed metabolic rate and weight regain. He did not, and so it was nice to see Dr. Hall setting the record straight in his most recent study. Dr. Hall's latest study now makes it clear that prior research (including his own) and clinical observations of people not losing or even regaining lost weight on reportedly very low calorie intakes which have contributed to the widespread belief that a slowed metabolism was the primary reason people hit weight loss plateaus and have trouble keeping off lost pounds was incorrect. In his new article, Dr. Hall states: "This [prior research] has led to speculation that the 6- to 8-month weight plateau may be due entirely due to the slowing of metabolic rate rather than loss of diet adherence. Our [new] results suggest otherwise and further illustrate that self-reported energy measurements are quantitatively unreliable." He concludes: "While energy expenditure adaptations have often been considered the main reason for slowing weight loss and subsequent regain, feedback control of energy intake [via increased hunger/appetite levels] plays an even larger role and helps explain why long-term maintenance of reduced body weight is so difficult." [http://onlinelibrary.wiley.com/doi/10.1002/oby.21653/full or  http://onlinelibrary.wiley.com/doi/10.1002/oby.21653/epdf].Increased Hunger, Not Slowed Metabolism, is the Main Reason Diets FailUnderstanding this is important because focusing on ways to boost metabolism via drugs, supplements, and/or exercise are ignoring the main reason that calorie-restricted diets fail. So why has weight control failure ignored the primary role of increased appetite and focused instead on the far less important role of a slowed metabolic rate? It turns out that measuring metabolic rate accurately is now fairly routine but this is not the case for measuring energy intake. The truth is that people often grossly underestimate calorie intake, making diet logs and food frequency questionnaires nearly useless for reliably determining a person's calorie intake. Therefore, determining the relative role of increased hunger and food intake relative to the role of a slowed metabolic rate has been a challenge, largely because accurately measuring calorie intake of free living subjects has proven very difficult. In part this is because measuring daily calorie intake accurately is a challenge, but also unlike measuring metabolic rate (which varies little from day to day in weight-stable people) calorie intake varies quite a bit from day to day even in weight-stable people. Dr. Hall and his associates have recently developed an inexpensive mathematical method to precisely measure average calorie intake over the long term. [Sanghvi A, Redman LA, Martin CK, et. al. Validation of an inexpensive and accurate mathematical method to measure long term changes in free-living energy intake. Am J Clin Nutr 2015;102:353-8].  Research conducted by Dr. Eric Stice and others has shown that portion-controlled calorie-restricted diets not only increase appetite but also greatly increase the desire to eat more calorie-dense foods that are high in fat and/or sugar. [Stice E. et al. NeuroImage 2013;67:322-30 or https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3693571/]. Indeed, according to Dr. Stice, it is likely that self-imposed calorie-restricted diets may be a major factor triggering the development of eating disorders. Pitting a powerful biological drive such as hunger against one's intellectual will is in fact likely counterproductive for long-term weight control and may very well be a formula for frustration and disordered thinking about food along with sometimes distorted views of the body itself. Growing evidence suggests that eating disorders arise because of this conflict. Picture trying to limit urine output by measuring it and then stopping at some preordained "correct" amount that is well below what your body tells you to do. How long would your intellectual will to urinate less be able to override the powerful biological urge to urinate? Yes this strategy still requires some willpower, but in this case it is pitted against cravings for unhealthful fattening foods rather than against the powerful biological drive of hunger.Focus on WHAT People Eat Rather than HOW MUCH They EatAs Dr. Stice and colleagues have shown, the increased hunger seen with traditional calorie-restricted diet and exercise programs greatly heightened his subject’s desire to consume highly-palatable calorie-dense foods, thus making calorie-dense low-satiety-per-calorie (or fattening) foods far more difficult to avoid over the long term. A more rational approach to reducing calorie intake without increasing hunger is to simply focus change on WHAT people eat. By changing WHAT is consumed to a diet composed largely of minimally-processed plant foods such as vegetables, beans, whole grains, and fruit with a low to modest calorie density and high satiety/kcal, people will consume far fewer calories without any need to use their intellectual willpower to eat less than hunger demands. Indeed, Dr. Stice's research shows portion controlled diets actually greatly increase the desire to eat low satiety/kcal foods.Dr. Stubbs showed that healthy subjects consumed nearly 1500kcal more per day on average over two weeks when consuming the most calorie-dense diet than when consuming the least calorie-dense diet [http://www.nature.com/ijo/journal/v22/n10/pdf/0800715a.pdf or Stubbs, RJ, Johnstone AM, O'Reilly LM, et. al. The effect of covertly manipulating the energy density of mixed diets on ad libitum food intake in 'pseudo free-living' humans. Int J Obes. 1998;22:980-7]. Also needed for weight control without hunger would be cutting out most beverage calories as these too have been shown to provide less satiety per calorie. And finally, eating only when hungry and until comfortably full (not stuffed) is generally a good approach. Following those simple guidelines is a safer and more effective way to lose excessive body fat stores and improve one's health than by trying to fight hunger while eating low satiety/calorie foods and drinks. Yes, this strategy still requires some willpower, but in this case it is pitted against cravings for unhealthful fattening foods rather than against the powerful biological drive of hunger. There's a big difference between fighting both hunger and cravings versus cravings alone, which are typically far greater when people are hungrier. Plus, research has shown that cravings for drugs or fattening foods weaken over time and so less and less willpower is required to make healthful food choices. Increased Hunger Linked to More Calorie-Dense Food ChoicesA study conducted by Brian Wansink, Ph.D., and Aner Tal, Ph.D., of Cornell University, Ithaca, N.Y., suggested that hungry grocery shoppers tend to buy more calorie-dense products than shoppers who are not hungry. The research included a laboratory study in which 68 paid participants were asked to avoid eating five hours prior to the study, although during some of the sessions some of the participants were given crackers so they would no longer feel hungry. A follow-up field study tracked the purchases of 82 participants at different times of the day when they were most likely to be full or hungry. According to the results, hungry laboratory participants chose a higher number of higher-calorie products, but there were no differences between conditions in the number of lower-calorie choices and the total number of food items selected. Field study shoppers who completed the study at times when they were more likely to be hungry (between 4-7 p.m.) bought fewer foods that were lower in calorie density and more calorie-dense food options compared with those who went food shopping when they were less likely to be hungry. This shows that even short-term food deprivation and increased appetite can shift food choices so that people choose fewer low-calorie foods, and relatively more high-calorie (and so low satiety/kcal) food options. "The implications of this imaging study are crystal clear; if people want to lose excess weight, it would be more effective to consume healthy, low-fat/low-sugar foods during regular meals, rather than go for long periods of time without any caloric intake." explains Dr. Stice. [http://jamanetwork.com/journals/jamainternalmedicine/fullarticle/1685889].Bottom Line: The time has come to abandon the failed weight control paradigms of the past, which are based on erroneous assumptions about calorie counting and attempts to boost a slowed metabolism. Once you accept that diet and exercise programs fail largely because people get hungry, the primary target for the solution becomes clear. Focus on eating foods that provide more satiety per calorie. That means one should cut way back on beverage calories and consume mostly foods with a lower calorie density and higher fiber content. Calorie-dense foods are either dry or fatty and those that are both tend to be the most fattening because they provide the least satiety/kcal. Have clients eat only when hungry (not starved) and until comfortably full (not stuffed). One still needs willpower to avoid fattening (or low satiety/kcal) foods and drinks because such options are increasingly the norm in modern societies. But there is a difference between pitting willpower against the cravings or temptations to consume low satiety per calorie foods and pitting willpower against the powerful biological hunger drive. Trying to override hunger with willpower leads to weight control failure in most people sooner or later and sadly all too often in the most determined people traditional calorie restricted diet & exercise programs appear to be a major factor triggering the development of eating disorders.