The Pros and Cons of Aggressive Dieting [Calories Deficits #3]

In All Articles, Blog Posts by Danny Lennon3 Comments

This is part 3 of a series of articles on caloric deficits. Make sure to read parts 1 & 2:

  1. Calorie Deficits #1: Understanding the Nuances of Energy Balance
  2. Is Slow & Steady Actually the Best Way to Diet? (Calorie Deficits #2)

In part two of this series we discussed how fast rates of weight loss through large caloric diets CAN be used without loss much (if any) muscle mass. Especially in those with a decent amount of fat to lose.

So should YOU use an aggressive diet?

Let’s evaluate the pros and cons…

The Pros of Aggressive Dieting

Researchers at Pennington Biomedical Research Centre published a study  looking at the effect of caloric restriction on overweight individuals (Heilbronn et al., 2006). In that study 48 people were randomized to one of four groups for 6 months:

  1. Control = 100% of energy requirements (i.e. maintenance calories)
  2. Calorie Restriction (CR) = 25% reduction in calorie intake (diet restriction)
  3. Calorie Restriction + Exercise (CREX) = 12.5% decrease in calorie intake +1 2.5% increase in energy expenditure from additional exercise, giving a total 25% calorie deficit
  4. LCD = low calorie diet (890 kcal/d) until reaching a 15% weight reduction, then switched to maintenance intake to maintain weight

After six months the changes in body weight were:

  • Control = -1.0% (± 1.1%)
  • CR = -10.4% (± 0.9%)
  • CREX = -10.0% (± 0.8%)
  • LCD = -13.9% (± 0.7%)

Which graphically looks like this:

Taken from: JAMA. 2006 Apr 5; 295(13): 1539–1548. Copyright: PubMed Central

Taken from: JAMA. 2006 Apr 5; 295(13): 1539–1548. Copyright: PubMed Central

Whilst the researchers were aiming to look at the effect of caloric restriction on longevity and metabolic adaptations, for the purposes of this article we’re not so much interested in those aspects. Rather if we look at the group who underwent the most aggressive diet initially we see a couple of important things…

By the end of the 6 month period they had experienced more weight loss than the other groups who had dieted on a milder deficit. However, what is more interesting to me, is that they achieved this greater weight loss at the 6 month time-point despite actually only dieting on average of 8-11 weeks out of the 24 weeks of the study.

And to me, therein lies the potential benefit (for some people) of a more aggressive diet; you can get the fat loss phase done in a much shorter period of time.

And so I feel one of the most important deciding factors in how aggressive to diet lies in the individual’s psychology and preference:

  1. Do they find the idea of slightly under-eating for a long stretch of time something easier to do than drastic restriction? Then a milder deficit with an extended dieting period is probably best.
  2. Do they find the idea of slightly under-eating for a long stretch of time to be akin to a living hell and find doing shorter concentrated bursts of very restrictive dieting to actually be more psychologically appealing overall? Then an aggressive diet for a shorter window of time is best.

So really it comes down to selecting as much of a calorie deficit that is manageable for the individual in question. That includes being both psychologically “manageable” as well as physically manageable; how much of a deficit can they be put in without completely destroying training performance, recovery, mood, energy and ability to avoid breaking down and binge-ing.

The Cons of Aggressive Dieting

On the physiological side, data from Trembley et al. (2013) suggests that shorter (< 6 weeks) more aggressive dieting bursts lead to a greater decrease in resting energy expenditure that  those in which the diet was carried out over a longer period of time. So there is a sharper adaptation of the metabolism.

However, we must remember that the dieting duration should be decreased and so the diet can return to maintenance intake or above soon, which will reverse most of the metabolic adaptations that have occurred.

Taken from: Trembley et al., Int J Obes (Lond). 2013 Jun;37(6):759-64

Taken from: Trembley et al., Int J Obes (Lond). 2013 Jun;37(6):759-64

On the more practical side, the obvious downside to aggressive dieting is that you have to eat less food, do more activity or a combination of both. Less food isn’t fun. And therefore it’s more difficult in an acute sense.

Less food also means that you need to include more dietary restraint. So you by nature will have less flexibility with your food choices. You just can include the same foods (and/or portions) that you could if you used a more gentle caloric deficit.

Less food will decrease your maximum recoverable volume (MRV). You just can’t recover from training to the same extent as when you are on a higher caloric intake.


Who is an Aggressive Diet Potentially Best For?

  • Those with a high body fat percentage (especially if weight is driving health issues)
  • Those motivated strongly by early success
  • Those who prefer more restrictive diets for short periods in comparison to longer dieting periods on higher calories
  • Those who do not have an immediate athletic goal or have training performance as primary goal
  • Those with a strategy of how to transition to maintenance eating and good habits after the dieting phase

Summary of Calorie Deficits Series

Despite commonly repeated ideas, the following things are all TRUE:

  • Dieting does not inherently mean you lose muscle
  • You can build muscle in a caloric deficit
  • Energy balance describes how much energy will be stored/released in/from the body. Not how much fat (or muscle) will be lost/gained
  • For all intents and purposes, within the context of a prudently structured diet and training regime, energy balance (intake – expenditure) is still a decent metric to use to target either fat loss or muscle gain during periods where either of those is the goal
  • Slow, sustainable weight loss isn’t always best. Rapid, aggressive weight loss isn’t always best. Context matters, imagine that?!

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