Metabolic Adaptation and Buffer Zones/Ranges

Most people have a range (buffer zone) of calorie intake where increases or decreases of calorie intake within this range result in no meaningful change in bodyweight. The corollary of this is that calorie intake generally needs to be significantly lower than one would expect (not uncommon for females to have to diet on 1,000-1200 kcals/day and males to have to diet on 1,500-2,000 kcals/day) in order to yield consistent fat loss. It is common for someone new to dieting to think to themselves:

“It seems like I’m maintaining weight on “X” amount of calories per day. This must mean that if I decrease my calorie intake by 500 calories/day, I can lose 1 lb. of fat per week! (500 calorie deficit x 7 = 3,500 kcals. 3,500 calories equals about 1 pound (0.45 kilogram) of fat).”

No. That’s not the way this works. 

This also explains why after a diet—assuming a gradual increases in calorie intake and NO BINGING—bodyweight will remain stable (sometimes bodyweight will even drop slightly) while the person adds somewhere in the range of ~500-1,000 kcals to their lowest calorie intake that they were previously dieting on. More specifically, after a fat loss phase, when gradually increasing kcal intake while still in the buffer range, the metabolism seems to sometimes adapt and relatively overshoot, which results in a loss of BW/fat (not indefinitely though). To be clear: this isn’t the result of the whoosh effect/loss of water/decrease in cortisol or increased NEAT (constrained TDEE precludes this).

Let me illustrate with my own metabolism:

I can finish a lean mass gaining phase maintaining weight on about ~4,000 kcals/day. However, my metabolism will swiftly adapt—with no real meaningful change in bodyweight/fat loss—to a calorie intake between 2,200-4,000 kcals/day. It is not until my calories are lowered to around 1800-2000 per day that I can consistently lose fat. In fact, I can ride out an entire fat loss diet on 1800-2000 kcals/day. 

Refeeds and Fat Loss

There are many ways to incorporate refeeds into a fat loss diet. Instead of arbitrary refeed frequencies (e.g. once per week), I tend to like to set up a diet so that the client is dropping 1 lb. below baseline every 3-7 days (preferably 3-5), at which point I will throw in a refeed on that particular day. 

3,500-4,500 kcal refeed days (biasing towards simple high glycemic index carbs) seems to be a good range to shoot for—not too conservative where the refeed just feels like a tease with no benefit on muscle retention, psychological satisfaction, paradoxically facilitating fat loss; and not too excessive where it would take too many days for bodyweight to baseline and also leaving the athlete feeling disgustingly bloated/full/gassy, lethargic (constantly wanting to nap), brain fog, inability to concentrate, unproductive all day, interfering with training, insomnia. Many will find that controlling for kcals, proportionally higher carb refeeds allow them to dip below baseline faster than higher fat refeeds.

At the end of a diet—when an athlete is very lean—I may throw in refeed days every time they dip 0.5 lbs. below baseline (instead of 1 lbs. below baseline).

Refeed days are not necessary if you are in a lean mass gaining phase. In fact, they are probably counterproductive leading to unnecessary fat gain. 

Are Calorie Intake and Cardiovascular Exercise Interchangeable?

The contribution of cardiovascular exercise and NEAT (non-exercise activity thermogenesis) to TEE (Total Energy Expenditure) hits the point of diminishing returns quite swiftly. 

Refer to study below:

https://www.ncbi.nlm.nih.gov/pubmed/26832439

"Here we tested a Constrained total energy expenditure model, in which total energy expenditure increases with physical activity at low activity levels but plateaus at higher activity levels as the body adapts to maintain total energy expenditure within a narrow range. We compared total energy expenditure, measured using doubly labeled water, against physical activity, measured using accelerometry, for a large (n = 332) sample of adults living in five populations. After adjusting for body size and composition, total energy expenditure was positively correlated with physical activity, but the relationship was markedly stronger over the lower range of physical activity. For subjects in the upper range of physical activity, total energy expenditure plateaued, supporting a Constrained total energy expenditure model.

Models of energy balance employed in public health should be revised to better reflect the constrained nature of total energy expenditure and the complex effects of physical activity on metabolic physiology.”

What might explain why this happens? Could be due to reduction in non-muscular physiological activities: reproductive activities, somatic maintenance, inflammation, etc. 

An argument can be made that past a certain intensity threshold (e.g. Michael Phelps, Lance Armstrong, etc.), constrained total energy expenditure may not apply. However, most people are either not willing or unable to perform at this intensity level for extended periods of time. You should also take into account how this could impact recovery and muscle retention. 

With regards to TEE, comparing cardiovascular exercise to total calorie intake is like comparing apples to oranges. They are not interchangeable. 

Does constrained total energy expenditure apply to decreasing calorie intake (as opposed to increasing cardiovascular exercise)? In my experience, no. 

The takeaway is that—with regards to fat loss—manipulating nutrition is going to be much more effective than increasing cardiovascular exercise.

I generally start clients on a resistance training regimen of 4-5 days/week with cardiovascular exercise set at no more than 30 minutes per day (moderate intensity).