Why Big Caloric Deficits and Too Much Cardiovascular Exercise Can Hurt Fat Loss

I recently discovered a case-study from 2004 that caught my attention.  In it, a 51 year old female began marathon training along with a (self-reported) low calorie diet and either appears to have gained weight or not lost weight (she also showed a very depressed metabolic rate).

In the study, the woman eventually raised her calories gradually, and as a result her body fat came down and her metabolic rate increased.  One oddity that I’ve seen (and personally experienced) over the years is one where the combination of very large caloric deficits and very large amounts of cardiovascular exercise can cause problems for people by either stalling or slowing fat loss. This is one of those oddities that seems to crop up more often than you’d expect.  It’s also one where there’s not a ton of research but I will happily provide a good bit of speculation on what I think may be going on.

I’d also note that the combination of big caloric deficits and large amounts of activity clearly isn’t detrimental to everyone.  Some folks can get away with it but, for many, it tends to backfire more than anything else.

First, Some Background

Back when I first became a trainer about 15 year ago, I had a client who was an older woman in her early 50’s who was determined to lose fat at any cost. She started working with me, and immediately jumped into something like 2 hours of cardio per day and cut calories massively.  She took in 1,000 calories per day, against my wishes, and it was insane (breakfast was supposedly one-half an egg and to this day I’m not entirely sure how you eat half an egg).

Now, I didn’t know much at that point but I had this general idea that too much activity and too few calories was a bad thing.  She wasn't losing any weight and for weeks on end I entreated her to either cut her activity or raise her calories.  She adamantly refused; and would say “how could that possibly work?”  I tried to point out that what she was doing wasn’t working either and she could hardly do worse by trying something different but that line of logic went nowhere.

At one point she went on a cruise or a vacation or something.  And what do you think she did?  Exercised less and ate more like everybody does on vacation.  And she came back 5 pounds lighter.  “See, see.” I told her, “You ate more and exercised less and good things happened.”  She eventually realized that more cardio wasn't benefiting her at all and began to cut her cardio in half while at the same time gradually increasing her calories and guess what? She ended up hitting her goal of losing weight and learned a valuable lesson along the way.* Results may vary upon the individual.

Another client I had a few years back was a 45 year old male who was overweight with the majority of his body fat centered around his midsection.  He had a history of “chronic yo-yo dieting”, having lost weight on a 6 month Metafast Weight-Loss Program (His particular Metafast weight-loss program consisted of drinking 3 meal replacement shakes per day, for a total daily caloric intake of 600 calories; very bad!).

So I met him a few months after he had lost a significant amount of pounds and regained it al.(He regained the weight 3 months following the conclusion of his 6 month/weight loss experiment *) The interesting part was when he completed the Metafast plan, he reportedly only took in 1,200 calories per day as maintenance and still managed to regain weight over the next 3 months!! *

On top of the 1,200 calories he took in for maintenance, he was jogging on average 3 miles per day, 6 days per week. So it wasn't like he returned to gluttonous eating and gorged on McDonalds 3 times per day, he actually continuing eating a very healthy diet consisting of lean proteins, healthy vegetables and a small amount of healthy fats. But his metabolism was damaged and he wasn't going to outsmart his metabolism again.

He was willing to do anything so I slowly increased his calories by having him add additional snacks between meals consisting of almonds, nuts, and MCT Fats.  I also gradually decreased his running to 3 days per week from 6 days, and had the 3 days of running with an emphasis on more of a high intensity interval approach.  I also include a “re-feed day” once per week, and it consisted of eating whatever he wanted but the catch was he could only do this during a 3 hour stretch during the “re-feed day”. It was more equivalent to a re-feed meal rather than a re-feed day.

At first he was terrified to raise his calories and dramatically cut his cardiovascular activity in half, but after the first few days he quickly noticed his scale weight dropping and his waist circumference decreasing. He continued to drop weight over the next 6 months and his waist circumference steadily declined until he reached healthy proportions. His metabolism was rebuilt! *

What’s Going On? Let’s Talk About Cortisol

Cortisol is one of those hormones that I imagine everyone reading this has heard about and about which a lot of misinformation exists.  Simply cortisol is a stress hormone, released by the body in response to nearly all kinds of stress.  In the fitness world cortisol has gotten an almost exclusively negative reputation (cortisol is ‘bad’ in the way that testosterone and thyroid are ‘good’) although this is simplistically incorrect.

Rather, whether cortisol does good things or bad things in the body depends on how it’s released.  Acute pulses of cortisol tend to do good things and be adaptive, while chronic elevations in cortisol tend to be bad and be maladaptive.

For example, the morning cortisol pulse helps to promote fat mobilization.  In contrast, a chronic elevation of cortisol (especially in the face of high insulin levels) tend to promote visceral fat accumulation.  As a non-fitness related topic, acute pulses of cortisol tend to be good for memory (why we often remember stressful situations in such detail) while chronic elevations (as often seen in depression) make memory go down the toilet.  And there are endless other examples of where acute cortisol pulses are good and chronic elevations are bad.

In any case, dieting in general is a stress.  And of course training is a stress.  And the more extreme you do of each, the more of a stress occurs.  And I suspect that a lot of what is going on when folks try to combine excessive caloric deficits with massive amounts of activity is that cortisol just goes through the roof.  Simply, you get these massive chronic elevations in cortisol levels.

This is also one reason I suspect that various types of cyclical dieting help with some of this issue.*  For at least brief periods, when calories are raised to maintenance or above, you break the diet/training induced elevations in cortisol.  This of course assumes that the person isn’t mentally stressed during the caller raising process.

So Why is This Bad?

As noted above, chronic elevations in cortisol can cause a lot of bad things to happen. One of them is simply water retention and water retention can mask fat loss, sometimes for extremely extended periods. I suspect that when people go on vacation and go off  their diet and come home down a few pounds on the scale, some of the scale weight loss is actually just water loss.

When calories are raised, cortisol mediated water retention dissipates.  Also educing total training (volume, frequency, intensity or some combination) does the same thing, which happens when clients I train go on vacation, they always come back lighter. (But this is only true for those who are really dedicated to their training and nutrition prior to vacationing, and have been stuck in a weight loss plateau)

But that’s probably not all of what’s going on.  Another effect of chronically elevated cortisol levels is leptin resistance in the brain.  Leptin is a hormone made in the fat cells that helps regulate energy balance in the body by inhibiting hunger and it plays a crucial role in weight control.

It is often referred to as the starvation hormone, since its main objective historically is to prevent human beings from starving do death during large periods of famine  If the brain senses that starvation is present and you are being underfed and undernourished, it will slow down metabolic rate, increase hunger and increase fat storages.

Leptin resistance occurs when the leptin signal is blocked. When the normal leptin signal to the brain is blocked, a lot of things can go wrong metabolically and I suspect that this is part of the problem.  When the brain does not hear a signal by leptin, which happens during leptin resistance, the brain assumes starvation is present and it immediately slows down metabolism, increases hunger and commands the food ingested to be preserved and stored as fat.

Although not necessarily related to cortisol, at least one study found that the addition of 6 hours per week of aerobic activity to a very low calorie diet (in this case a protein sparing modified fast) caused a larger decrement in metabolic rate than the diet alone.  The body appears to monitor caloric availability and if it gets too low, bad things can happen. *

This is why I so strongly suggested AGAINST the inclusion of too much cardio as it causes more harm than good. The biggest source of failure on my plans is when people ignore my advice and try to do a bunch of cardio. And fat loss stops.

In any case, there are several different plausible mechanisms by which the combination of excessive caloric deficits an large amounts of activity can cause problems.  Whether it’s simply cortisol related water retention, a drop in metabolic rate due to leptin resistance or something else, something is going on.  For a lot of people, the combination simply doesn’t work.  Mind you, some seem to get away with it but not all. *

An Additional Variable

There is another variable that I have noticed over the years in looking at this issue.  As odd as it sounds, it has to do with personality.  I have noticed that the people who seem to have the biggest issues with the whole lots of cardio/big caloric deficit tend to be a little bit ‘tightly wound’ (to put it politely). * A bit less politely they are stress cases.

When fat loss stalls for a day, they freak out and want to cut calories or go add another hour of cardio.  You can almost ‘see’ the tension in them as they sit hammering at the keyboard looking for solutions.  And this is an issue because these types of folks already over-secrete cortisol.

On the opposite end of the spectrum I have seen the most dramatic body transformations in clients that were more of the  “happy go lucky” type of personality.  These personality types never question the eating plan or spend endless hours looking for data online that may contradict my plan and its effectiveness.  These “easy going” types usually drop massive amounts of fat and I have had somer of my best transformations with these people. *

These people don't have expectations of the weight loss nor do they have a timeline of when it should come off.  They usually trust the process and are robotic about the entire process. They have healthy cortisol production and don't overreact to any situation. I could line up my most successful client transformations and the majority would be of this “happy go lucky” type of personality. Coincidence?

Basically, there is a subset of folks who are already high-level stress cases. They tend to be drawn to harder is better in the first place, tend to be resistant to change and their already high level of cortisol production is simply amplified by the combination of too much activity and too few calories.  And suggestions to raise calories and/or reduce activity are invariably met by resistance.  What they really need is to just chill out.

Moderate caloric deficits and moderate activity always work better in those folks. It’s getting them to do it, that’s the hard part!

Summing It Up

So there it is. We took a look at one of the oddities of fat loss, the situation where the combination of excessive caloric deficits and excessive amounts of activity seem to hurt rather than help fat loss, along with some speculation (and just enough research to make it sound like I know what I’m talking about) on what may be going on.

In a practical sense, of course, most of the background isn’t very relevant.  The simple fact for the majority of folks is this: you can either cut calories hard OR do large amounts of activity. But you can’t do both. Well you can do both, you just probably shouldn’t under most circumstances. * Results may vary upon the individual

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