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17 December 2019

Can aggressive periods of dieting actually be better than moderate? Were we wrong?

by Jackson Peos 0

If you consider yourself a player on TEAM “Evidence-based”, you are no doubt familiar with the prudent recommendation to adopt slower rates of weight loss as opposed to severe when embarking on your fat loss escapades. ‘Slow and steady wins the fat loss race’ Surprisingly, this recommendation is based largely on logical reasoning and a…

If you consider yourself a player on TEAM “Evidence-based”, you are no doubt familiar with the prudent recommendation to adopt slower rates of weight loss as opposed to severe when embarking on your fat loss escapades.

‘Slow and steady wins the fat loss race’

Surprisingly, this recommendation is based largely on logical reasoning and a pioneering study by Dr Ina Garthe on a small cohort of Olympic athletes, as opposed to a comprehensive body of research. However, given the number of parrots living inside the aviary we call Instagram, the “slower rates of weight loss are better” proclamation has been regurgitated so recurrently across the cages of social media, that it is now accepted as indisputable fact.

But should that really be the case?

Do we really understand the long-term effects of severe versus moderate dieting on lean mass and other aspects of body composition?

Should severe dieting or more rapid rates of weight loss be avoided at all costs?

A brand-new study coming from an Australian research group adds some spice to our research broth.  

Let’s start with what we think we know.

In 2011 a study was published led by Dr Ina Garthe, showing that 0.7% loss of body weight per week was preferable to 1.4% per week. The slower weight loss group lost just as much fat as the fast group but retained more lean mass and some measures of performance. 

Additionally, in the evidence-based recommendations for natural bodybuilding preparation review by Dr Eric Helms, 0.5-1.0% body weight losses per week are advised to minimise lean tissue loss and performance impairment.  

From a logical point of reasoning, slower weight loss recommendations make sense. It is conceivable that a weekly ceiling of achievable fat loss exists, with weight losses beyond that point arising from metabolism of lean tissues. It is also reasonable to assume that being too aggressive in your weight loss efforts could mean insufficient energy intake to support training and performance, and important physiological processes (e.g. menstruation for females). 

What can we learn from this new study?

We know the severe dieting periods can be a very effective treatment for obesity (google Very-Low-Energy-Diets for more research on this strategy). However, less is known about the potential downsides of severe diets on body composition and other outcomes, particularly long term.

To figuratively stick a sausage in the bun that is our gap of knowledge, the researchers recruited 101 overweight women aged 45-65, currently performing less than 3 hours of physical activity per week. They were randomly allocated to either 12 months of moderate dieting (25-35% deficit) or 4 months of severe dieting (65-75% deficit) followed by 8 months of moderate dieting.

At the end of the 12 months, we saw some pretty groovy things. 

Key findings

  • The severe dieting group lost more weight than the moderate group; -6.6kg
  • The severe dieting group lost roughly double the fat compared to the moderate group
  • The severe group decreased waist circumference and ab fat tissue volume by almost double the moderate group
  • 41/50 participants in the severe dieting group lost >10% of their body weight versus 14/51 in the moderate group
  • The severe group lost more lean mass than the moderate group; -1.2kg
  • When accounting for loss of total body weight, the severe group had only lost more lean mass after month 4, not 6 or 12
  • The severe group had greater thigh muscle size losses than the moderate group; -4.2cm
  • When accounting for loss of total body weight, the severe group had only lost more thigh muscle after month 4, not 6 or 12
  • No differences in handgrip strength between the groups
  • The severe group lost more bone mineral density in the hip than the moderate group
  • Significant increase in participants with osteopenia in the severe group but not the moderate group
  • 6 adverse events in the severe group versus 2 in the moderate group
  • 3x less likely to drop out of the severe group compared to the moderate

Bringing it all together

This study (which we can rely on with a decent degree of confidence due to the large cohort size, well-renowned research team and high-impact journal publication) tells us that starting off a weight loss phase with a period of severe/aggressive dieting may provide notable benefits.

Compared to dieting conservatively the entire the time, the group who dieted aggressively for the first third of the intervention lost twice as much fat and weight, and had a healthier fat distribution indicated by twice the loss of waist circumference, waist-to-hip ratio and abdominal fat tissue volume, both subcutaneous and visceral. Additionally, the findings suggest you are less likely to quit your weight loss phase after a period of severe dieting, likely due to the encouragement and motivation arising from the large and more rapid scale movements early on.

This method of dieting, however, is not without downsides. The severe group saw 1.5x greater losses of lean mass and thigh muscle area compared with consistent moderate dieting over 12 months. It’s worth point out however that this is before accounting for the greater loss of total weight in the severe group. It’s rational to assume greater losses of total body weight will be accompanied by greater losses of lean weight. It’s also worth noting that there were no differences in handgrip strength between the groups, so the impact of weight loss speed on performance outcomes might not be as significant as some suppose…yet this study was completed with a cohort of inactive overweight females, not athletes. Of more concern, is the 2.5x greater loss of bone mineral density in the severe group, irrespective of total weight loss. Therefore, caution should be applied when recommending severe diets to the broader population, particularly to those at risk of osteoporosis.

Closing

I think this study tells us that things aren’t as simple as “fast = bad” “slow = good” when it comes to advisable rates of weight loss, despite what the Instagram parrots will tell you. Double the fat loss in the same timeframe, better fat distribution, 3x less likely to quit the diet…these are huge takeaways which challenge the status quo. 

Yes there are some downsides, but unless you are at risk of bone density related issues, at worst you are looking at greater absolute losses of lean mass…which are in proportion to the greater amount of weight and fat you can lose with a severe burst of dieting.

Clearly body composition goals come into play here when discussing practical applications of the findings. If fat loss is prioritised above maximising lean mass, then you can potentially double your fat shreds with a little extra grinding. Throwing in a severe block of dieting might do you a world of good.

If you have to slog through the mud for every milligram of lean mass, then you’re probably not too keen on the idea of giving that up. In that case, perhaps less fat loss, but potentially greater lean mass retention is a more viable option for you, and you might elect to skip on the severe block of dieting.

In my opinion, I think most people would benefit from a more severe block of dieting than is typically recommended in our fitness community though. Of course, there’s some nuance within that statement. This study was completed on overweight females remember. It’s very possible, and rational, that leaner training athletes might have more upside to being conservative with their rates of weight loss given the requirements to fuel performance, and the greater susceptibility to lean mass losses at a leaner body composition.

It would be great to see in the future a comparison between body composition responses of lean versus overweight people following aggressive or moderate rates of weight loss.

(Don’t scoop my study idea)

Jackson Peos PhD (c)

Reference

https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2753660

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