MedicalResearch.com Interview with:
Professor Nuala Byrne PhD
Head of School | Health Sciences
Faculty of Health
University of Tasmania
MedicalResearch.com: What is the background for this study?
Response: Calorie restriction (or cutting back on the energy we are eating) triggers powerful compensatory responses by our body’s metabolism – we might think of it as a “Famine Reaction”. Our body weight is regulated by a series of nervous system and hormone networks that act together to make sure we have enough energy to sustain life. When we eat more energy than our body needs to meet our daily metabolic requirements (positive energy balance), we are designed to store that excess energy; and we are very good at storing. We store this energy in the fat cells (adipocytes) as an emergency reserve for when we hit hard-times when food availability is scarce. The problem in today’s society is that most of us have a constant availability of energy-dense food; making it more common to be in energy excess.
When we have less calories being consumed than what we need to fuel all the body’s metabolic processes (negative energy balance), we convert the stored fat into usable energy, and consequently lose weight. While our body does sense the positive energy balance, it is designed to be more sensitive to gauging when we are in a negative energy balance. Our body senses the change in energy intake and the decreasing fat stores, and brings out the artillery to defend our energy stores – this is the Famine Reaction. Our body is constantly changing our physiology in response to challenges to the status quo; the body works constantly to keep the oxygen concentration in the blood at an optimal level, to keep a constant and optimal body temperature, and a constant and optimal amount of sugar in the blood. Our body’s regulatory systems also work hard to defend our energy stores if it senses we are continually in negative energy-balance (i.e., dieting). One major metabolic compensatory as part of the “Famine Reaction” is a decrease in the body’s resting metabolic rate (energy expended while at rest to maintain the basic functioning of our major organs). Given that resting metabolic rate is determined largely by body size and composition, it is expected to decrease with weight loss. However, during dieting, resting metabolic rate has been reported to decrease to a greater extent than that expected from changes in body composition, a phenomenon termed ‘adaptive thermogenesis’. This leads to markedly reduced efficiency of weight loss.
Importantly though, despite the adaptive compensations to dieting, many of these responses can be reversed following a 7- to 14-day period of energy balance post-weight loss. This raises the possibility that periods of deliberate energy balance could be exploited during dietary interventions to enhance the efficiency of weight loss. This approach is akin to periodisation in exercise training programmes which incorporate stimulus cycles to progressively overload the physiology and stimulate positive adaptations in functional capacity, and cycles of reduced training volume designed to avoid overtraining and the negative effects on performance that result from chronically high training loads. In a similar way, an intermittent approach to dieting, consisting of cycles of restriction interspersed with periods of energy balance, may attenuate compensatory responses associated with chronic energy restriction, and thus provide a more effective and sustainable weight loss strategy than traditional continuous approaches.
MedicalResearch.com: What are the main findings?
Response: We proposed that an optimal intermittent energy restriction cycle might be to combine 2-week blocks of energy balance (sufficient time for the attenuation of adaptive thermogenesis) with energy restriction (dieting) blocks of the same length. The aim of this investigation was to compare changes in body weight, body composition, and resting metabolic rate in men with obesity in response to: (1) 16 weeks of continuous dieting (33% energy intake reduction below weight balance requirements), or (2) an equivalent duration and magnitude of energy restriction delivered intermittently as alternating 2-week blocks of energy restriction and energy balance.
We found that intermittent energy restriction (dieting) resulted in greater weight loss and greater fat loss, without greater loss of lean tissue, than an equivalent ‘dose’ of continuous dieting.
In addition, despite greater weight loss, there was a significantly smaller reduction in relative resting metabolic rate in the intermittent dieting group, consistent with attenuation of adaptive thermogenesis. Furthermore, although both groups regained weight post-intervention, weight loss (reduction from baseline) was, on average, 8 kg greater in the intermittent group compared with the continuous dieting group at the 6-month follow-up.
MedicalResearch.com: What should clinicians and patients take away from your report?
Response: Part of the difficulty in achieving lasting weight loss by lifestyle changes such as “dieting” is that the body responds to calorie restriction through a series of compensatory changes in the body’s metabolic processes; and this occurs to everyone, no matter what weight we start at. So, although there is some truth to the fact that our metabolism can work against us when we try to lose weight, this doesn’t mean we can’t be successful in long-term weight loss, we just need to have a better understanding of how the body works.
While we need to understand more regarding the mechanisms (biological and behavioural) upon which this 2-week restriction & 2-week balance improves weight loss, these findings provide preliminary support for the model as a superior alternative to continuous dieting.
MedicalResearch.com: What recommendations do you have for future research as a result of this study?
Response: While there is great promise in the findings from the current study, we have more to learn in order to optimise the approach. We want to understand more detail to improve how we can work with biology rather than against biology to enhance weight loss success. We also need to understand the behavioural and psychological strategies that improve weight loss success.
MedicalResearch.com: Is there anything else you would like to add?
Response: We need to respect the amazing biological defense mechanisms utilized by the human body to protect against rapid weight loss; it is the reason why we are here as a species having survived many famines in millennia past.
We also need, as scientists and clinicians, to take the time to develop a robust evidence base upon which to recommend appropriate weight loss strategies. As a scientific community, we must resist the urge to promise ‘solutions’ and write ‘how to’ books that recommend strategies that are not adequately researched.
It is also important to accept that there will be no ‘silver bullet’ weight loss solution, and it is highly unlikely that a one-strategy-fits-all approach will effectively address the challenge in achieving long-lasting weight loss.
MedicalResearch.com: Thank you for your contribution to the MedicalResearch.com community.
N M Byrne, A Sainsbury, N A King, A P Hills, R E Wood. Intermittent energy restriction improves weight loss efficiency in obese men—The MATADOR study. International Journal of Obesity, 2017; DOI: 10.1038/ijo.2017.206
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