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Yo-yo dieting might cause extra weight gain

Repeated dieting may lead to weight gain because the brain interprets the diets as short famines and urges the person to store more fat for future shortages, new research by the universities of Exeter and Bristol suggests.

“Non-dieters learn that the food supply is reliable so there is less need for the insurance of fat stores.”

This may explain why people who try low-calorie diets often overeat when not dieting and so don’t keep the weight off.

By contrast, people who don’t diet will learn that food supplies are reliable and they do not need to store so much fat.

The study, published in the journal Evolution, Medicine and Public Health, is based on observations of animals such as birds.

Animals respond to the risk of food shortage by gaining weight, which is why garden birds are fatter in the winter when seeds and insects are hard to find.

The authors studied a mathematical model of an animal that knows whether food is currently abundant or limited, but does not know when things will change, so must learn about the changeability before deciding how fat to be.

The model shows that if food supply is often restricted (as it is when dieting) an optimal animal — the one with the best chance of passing on its genes — should gain excess weight between food shortages.

Dr Andrew Higginson, Senior Lecturer in psychology at the University of Exeter, says: “Surprisingly, our model predicts that the average weight gain for dieters will actually be greater than those who never diet.

“This happens because non-dieters learn that the food supply is reliable so there is less need for the insurance of fat stores.”

With more and more people becoming obese, scientists are looking for evolutionary reasons to explain why many find it hard to resist overeating.

Humans evolved in a world where food was sometimes plentiful and sometimes scarce — and in the latter case those with more fat would be more likely to survive.

Today, people can get into a vicious cycle of weight gain and ever more severe diets — so-called yo-yo dieting — which only convinces the brain it must store ever more fat.

“The brain could be functioning perfectly, but uncertainty about the food supply triggers the evolved response to gain weight.”

The researchers’ model predicts that the urge to eat increases hugely as a diet goes on, and this urge won’t diminish as weight is gained because the brain gets convinced that famines are likely.

“Our simple model shows that weight gain does not mean that people’s physiology is malfunctioning or that they are being overwhelmed by unnaturally sweet tastes,” says Professor John McNamara, of the University of Bristol’s School of Mathematics.

“The brain could be functioning perfectly, but uncertainty about the food supply triggers the evolved response to gain weight.”

So how should people try to lose weight?

“The best thing for weight loss is to take it steady. Our work suggests that eating only slightly less than you should, all the time, and doing physical exercise is much more likely to help you reach a healthy weight than going on low-calorie diets,” Dr Higginson says.

Story Source: University of Exeter.


Journal Reference:

  1. A. D. Higginson and J. M. McNamara. An adaptive response to uncertainty can lead to weight gain during dieting attemptsEvolution, Medicine and Public Health, December 2016 DOI: 10.1093/emph/eow031
Significant progress against HIV epidemic in Africa

HIV 90-90-90 goals are in reach in Zimbabwe, Malawi, and Zambia, say researchers, adding that new infections are falling.

The percent of the population infected with HIV is stabilizing, and over half of all people living with HIV are virally suppressed, the investigators have found.

The effects of HIV have been far-reaching. But these outcomes affirm that global, country, and U.S.-supported HIV efforts have been successful to date,

National surveys in Zimbabwe, Malawi, and Zambia reveal exceptional progress against HIV, with decreasing rates of new infection, stable numbers of people living with HIV, and more than half of all those living with HIV showing viral suppression through use of antiretroviral medication. For those on antiretroviral medication, viral suppression is close to 90 percent. Thirty-five years into the global HIV epidemic, these findings are a clear sign of progress and source of hope for the rest of the world.

These data are the first to emerge from the Population HIV Impact Assessment (PHIA) Project, a unique, multi-country initiative funded by the U.S. President’s Emergency Plan for AIDS Relief (PEPFAR). The Project deploys household surveys, which measure the reach and impact of HIV prevention, care and treatment programs in select countries. ICAP at Columbia University is implementing the PHIA Project in close collaboration with the U.S. Centers for Disease Control and Prevention (CDC) and in partnership with ministries of health.

Importantly, the data positively demonstrate that the 90-90-90 global targets set forth by UNAIDS in 2014 are attainable, even in some of the poorest countries in the world. According to these ambitious targets for 2020, the goal is for 90 percent of people with HIV to be diagnosed, 90 percent of those diagnosed to receive HIV treatment, and 90 percent of those on treatment to be effectively treated and achieve suppression of their infection. This would translate to 73 percent of all HIV-positive people being virally suppressed. The data show that once diagnosed, individuals are accessing treatment, staying on treatment, and their viral load levels are suppressed to levels that maintain their health and dramatically decrease transmission to others.

“The effects of HIV have been far-reaching. But these outcomes affirm that global, country, and U.S.-supported HIV efforts have been successful to date, and that strong progress is being made across the entire HIV continuum of care, including excellent durability of first line treatment regimens with high adherence to medications,” said Ambassador Deborah Birx, U.S. Global AIDS Coordinator.

The PHIA Project surveys describe national HIV epidemics by looking at HIV incidence (the rate of new infections), HIV prevalence (the percent of the population living with HIV), and the prevalence of viral load suppression (a measure of a well-controlled HIV infection), all through a nationally-representative sample of the population. Additional measures in the surveys look at the proportion of those with HIV who have been tested and who are on treatment.

The household surveys of approximately 80,000 adults and children in Zimbabwe, Malawi, and Zambia were conducted in 2016. Results show that the rate of new infections is less than one percent per year. HIV prevalence, at 10 to 14 percent, is similar to 2010 estimates, and more than half of all adults living with HIV have viral load suppression. Compared to 2003 incidence estimates for the same three countries of between 1.3 and 1.5 percent per year, the current rate of new HIV infections has been cut in half during the past 13 years, when effective HIV treatment became available in sub-Saharan Africa largely through support from PEPFAR.

“The survey was designed to identify the rate of new infections at the national level, as well as to estimate the number of people living with HIV,” said Dr. Jessica Justman, PHIA principal investigator and senior technical director at ICAP. “This information is critically important to determining future resource needs.”

Preliminary data analyses show that, as of 2016:

  • In Zimbabwe, among adults ages 15 to 64, HIV incidence is 0.45 percent; HIV prevalence is 14.6 percent (16.7 percent among females and 12.4 percent among males); 60.4 percent of all HIV-positive people are virally suppressed, and 86 percent of those on treatment are virally suppressed.
  • In Malawi, among adults ages 15 to 64, HIV incidence is 0.37 percent; HIV prevalence is 10.6 percent (12.8 percent among females and 8.2 percent among males); 67.6 percent of all HIV-positive people are virally suppressed, and 91 percent of those on treatment are virally suppressed.
  • In Zambia, among adults ages 15 to 59 years, HIV incidence is 0.66 percent; HIV prevalence is 12.3 percent (14.9 percent among females and 9.5 percent among males); 59.8 percent of all HIV-positive people are virally suppressed, and 89 percent of those on treatment are virally suppressed.

“The partnership with the ministries of health has been fundamental to the success of the surveys,” said Dr. Shannon Hader, director of the Division of Global HIV and Tuberculosis at CDC. “This kind of information has not been available before and the ministries are eager to use the survey results to inform their policies and programs.”

With high HIV prevalence estimates of 10 to14 percent, these three countries continue to bear a substantial HIV burden. Nonetheless, with prevalence stabilizing and incidence falling, the PHIA survey results suggest that people living with HIV are living longer thanks to effective and accessible treatment.

“It is heartening to see the impressive viral suppression noted in the three countries among those on treatment,” said Dr. Wafaa El-Sadr, global director of ICAP. “Viral suppression is critical for the well-being of people living with HIV and for preventing HIV transmission to others.”

The results from the first three PHIA surveys compel the global community to strengthen its efforts to reach those who have yet to receive an HIV test and to engage, support, and enable those who test HIV-positive to start and stay on effective treatment in order to achieve long-term viral suppression.

“Importantly, the PHIA surveys point to what still needs to be done, who we need to reach, and where we must focus our efforts, in order to build on these achievements,” Ambassador Birx added. “The findings will guide an effective response to the epidemic.”


Story Source: Columbia University’s Mailman School of Public Health.

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