Sustained Weight loss

Losing weight is no smooth ride, anyone who has done it, will tell you that it takes a lot of dedication, persistency, time, highs and lows (in terms of your daily energy, performance in the gym and, mood) and, being more hungry than usual (understandable! Lower calories). So overall, it takes a great deal of mental and physical willpower to make fat loss happen.

In terms of how these things during the fat loss process effect different people, will depend on the extent of the fat loss wanted, the duration, the diet and training program followed, your genetics (particularly in terms of metabolic efficiencies) and, how much you want it. As you can imagine, we are always looking for ways to smooth this process out, make it a lot more manageable and more importantly, make it sustainable. Pretty obvious, if you can’t maintain your program, then you will find it difficult to achieve the results you want! But, this is where leptin and refeeds might come into the picture: can they make weightloss more sustainable and, more effective over the longer-term? What does the science say?

So important questions to ask are:

Where does leptin and refeeds fit into the whole weight loss picture? 

What is leptin and why is it so important for weight loss?

What are refeeds and why do they have anything to do with leptin and weight loss?

What Is Leptin?

Firstly, there is a huge amount of research being done into leptin and it’s effects on human physiology in the context of weight loss (Here are a few recent studies you can dig into! Strohacker et al, 2014; Rosenbaum and Leibel 2014; Kisseleff et al, 2012). So, it’s a pretty big deal! Leptin’s role in the body is vastly multi-functional, it does a lot of stuff. It’s a big fish! It plays an important role in modulating energy homeostasis and metabolism (amongst a great deal of other things! (Interested in a general background over leptin and it’s functions then check out this article Mantzoros et al, 2011).  

So, what is leptin’s role in weight loss? Well firstly, it has been demonstrated that periods in energy-deficient states are accompanied by decreases in leptin concentrations in the body and that the drop in leptin is related to the reduction in ‘fat mass’ (Dardeno et al, 2010). Moreover, acute, short-term reductions in calorie intake (fasting) are related to increases in leptin concentrations out of proportion to fat mass (Chan et al, 2003).

The key take away from both these observations is that leptin reductions signal some kind of shift from ‘abundance’ to ‘scarcity/starvation’, driving your body to survival.

When leptin levels in the body change, a series of changes occur in the body that might make it difficult to lose further weight and/or keep the weight OFF. When concentrations of circulating leptin in your body change, the adjustment of various subsequent downstream physiological processes in the body can lead to changes in appetite, satiety (feelings of fullness), energy expenditures, cognitive control and behavioural inhibitions towards food and, mood, arousal and reward (controlling the incentive for food intake)(Dardeno et al, 2010). I guess then it’s safe to say that changes in leptin could cause a few things in your body to go haywire!  All part of the survival process!

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A study published by Hinkle et al, 2013 found that in obese participants that maintained a 10% reduction in weight, participants exhibited increased activity in the regions of the hypothalamus responsible for attentional, visual and reward processing in response to food cues (relative to non-food cues). Interestingly, when one of these groups were given leptin treatments (in comparison to the control group with just saline), researchers noticed in this group, changes in connectivity between the hypothalamus and certain brain regions that were responsible for ‘switching on’ energy intake regulation mechanisms, as well as down regulation of food-reward signals. 

The conclusion of the study? Researchers suggested that in reduced-weight maintenance individuals, the reduction in leptin switches energy homeostasis in favour of increased food intake and appetite.

On re-application of leptin, this increased ‘want and need behaviour towards food’ may be attenuated. Ultimately, behaviour is shifted towards ‘I want food so badly, food looks so good!’ in a weight reduced state. Which seems to be pretty accurate, right? I mean, there is a point reached when you are losing weight when all you can think about is food, and this tends to intensify the deeper you go into your weight loss program. I am sure most of you have experienced this? 

In another study that was published (Rosenbaum et al, 2005), researchers looked at three study groups (5 males and 5 females; 3 never obese and 7 obese): 1) maintaining their usual weight 2) maintaining a 10% reduced weight and 3) maintaining a 10% reduced weight, with everyday subcutaneous (injected under skin) administration of leptin to pre-weight loss levels.

It was found that leptin administration to pre-weight loss levels led to the restoration in energy expenditure declines, an increase in *SNS (sympathetic nervous system activity) and, circulating thyroid hormones.

*SNS activity restoration with leptin here was associated with an increase in heart rate and arterial pressure, epinephrine and norepinephrine, renal activity and, increase in utilisation of brown adipose tissue. Important because increased SNS-related activities can increase energy expenditure (calories burned) and thus potentially enhance fat loss over time. 

The conclusion of the study? In a reduced-weight maintenance state, a series of changes seem to take place in terms of energy expenditure, SNS activity and circulating metabolic hormones (e.g. thyroid hormones) that would favour ‘regain’ of weight lost. On application of leptin to reduced-weight maintenance participants, these changes seem reverse back to pre-weight loss levels. 

It’s worth mentioning that administration of leptin nearly 10-fold of normal circulating levels into normal-weight individuals did not have the same effect in the amplification of diverse physiological processes as seen above in those of maintained reduced-weight. This gave people the idea that leptin is not actually implicated in fat reduction itself but merely fat defence. In other words, below a certain ‘fat threshold’, the concentrations of leptin will reach a point in which the ‘survival mechanisms (physiological changes as observed above) will start to kick in (reduced energy expenditure, increased hunger levels, reduced satiety, changes in circulating thyroid hormones, behaviour changes in response to food etc.). The magnitude of which increases as more fat is lost and leptin concentrations drop further (Rosenbaum et al, 2005)

What does all this science tell us? 

Leptin is no bro-science! It’s present in the body and it’s really important for modulating our ‘behaviour’ towards food through diverse physiological processes 

Leptin depends on body fat. As you lose body fat, leptin concentrations in the body will lower (although an acute drop in energy intake regardless of amount of fat can actually cause a significant drop in leptin concentrations). 

Lower levels of leptin will lead to a range of physiological processes that signal a shift from ‘everything is good’ (abundance) to ‘no food!!!’ (Scarcity). This will include reduced energy expenditures, reduced satiety, increased hunger, changes in circulating hormones, changes in SNS activity and activity in certain brain regions (mood, behaviour, need towards food) . 

Leptin doesn’t actually reduce fat, but it might help us ‘maintain’ the weight we have lost and continue on that path (provided you can find some way of raising leptin). 

Extra leptin in those of normal weight has no influence. Sorry folks! 

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Leptin And The Case For Refeeds?

Refeeds are something you hear about often in the fitness world, especially when someone is on a calorie-restricted nutrition plan. But what exactly do they mean? Well simply, refeeds are just periodic points in your calorie-restricted nutrition plan where you temporarily bring your calorie intake back up to maintenance (or just above). How people actually structure their refeeds can vary massively, but typically a refeed might last 24 hours, and might occur once or twice per week depending on where you are in your weight loss plan (Trexler, Ryan and Norton, 2014). If you have lost a lot of weight and you are ‘deep into a cut’ then more regular refeeds might be beneficial. But it all depends! So, what is the connection between leptin and refeeds?

Interestingly, science has found that these refeeds (predominantly through increasing your carbohydrates) can actually boost the levels of circulating leptin during weight loss, temporarily (Trexler, Ryan and Norton, 2014). Although the research is pretty scare when it comes to the link between the benefits of refeeds, leptin and weight loss, there are a few things that are worth considering given the current research:

When fat levels decrease, leptin levels decrease. This causes a series of changes such as reduced energy expenditure, changes in metabolic hormones, SNS activity, behavioural changes, increased hunger and, reduced satiety. These effects appear to intensify as more fat is lost.

If refeeds can temporarily boost leptin and attenuate these responses (especially the bouts of intense hunger and low energy at low body fat levels!), this might help increase adherence to a weight loss program (particularly when you are at extremely lot levels of body fat or heaving close to it). But, there are a few things to consider:

This would probably depend on how much fat someone has lost since starting their fat loss program. Considering the extent of fat loss, most people might not even need a refeed. This is because leptin levels simply might not be low enough to make these physiological changes strong enough that could begin to effect adherence. Only when someone is trying to get into the realm of very low body fat percentages might this refeed principle hold value. For most people outside the realm of say competing (e.g. bodybuilding), refeeds might not be needed.(But there is no solid science to back this up, this is just me making a logical connection with what we have!). 

There is no long-term data on refeeds and leptin. Essentially, we do not know what the long-term effect would be on weight loss with periodic refeeds over time. We know a refeed (particularly one high in carbohydrates) increases leptin, and we know low levels of leptin can reduce our energy expenditures through different mechanisms. But that’s it. What is the long-term effect on metabolic rates through periodic refeeding? We don’t know! 

The bottom line?

There isn’t a lot to go on at the moment. But there is something there with regards to refeeds and leptin, we just have to wait for more research! At this time, I believe that, with the research we do have, high-carbohydrate periodic refeeds do hold value for those who are looking to achieve very low levels of body fat. Periodically raising leptin is likely to keep at bay the intense hunger feelings, low energy and feelings of never being full that one experiences at this level, at bay (in turn helping them to maintain progress and the weight loss they have achieved! If it prevents those binges and regressions, then refeeds it is!).

For those who are just looking for a moderate degree of weight loss, refeeds might not be needed. However, even here, refeeds might still offer some benefit to these people, not in terms of needing to raise leptin, but simply the whole ‘giving you a diet break’. If a slight periodic bump in your daily calories helps (maybe call it here a ‘bump-feed’ rather than a refeed, something more moderate) keep you on track and maintain the progress you have made, then maybe it’s not such a bad idea. As far as ADHERENCE goes rather than any metabolic benefits. 


Any questions, ask away!