The idea of spot reduction, reducing body fat in a specific area with exercise, is one that has floated around the fitness body recomposition world for decades. Men want the ever desirable six-pack and can be seen doing abs until the cows come home while women try to slim hips and thighs with endless reps on the inner/outer thigh machine.
Exercise classes pander to this, offering hour long “abs” or “buns/thighs” classes which usually consist of a billion reps of movements that work the target area. Even in the bodybuilding world, where people really should know better, some still argue that spot reduction can occur and that working a given muscle group will help reduce fat in that specific area. I addressed this topic somewhat in The Stubborn Fat Solution since some of what I discuss in that book could readily be confused with spot reduction even though it’s really not.
So today I want to take a brief look at the topic of spot reduction, primarily by examining a paper that has been making the rounds as an argument that spot reduction exists. That paper is:
What is Spot Reduction?
As above, the general idea of spot reduction is that doing exercise for a given area will reduce body fat preferentially in that area. So if the goal is to reduce abdominal fat, abdominal exercise would be done. To reduce the hips and thighs, hip and thigh exercises would be done. Men who are trying to reduce their love handles do endless side bends and women who want to reduce back of the arm triceps fat do endless kickbacks and pushdowns.
While being admittedly snarky, I’ve often asked “If spot reduction works, why don’t people who eat a lot have skinny faces?” Yes, it’s a bit silly but I’m primarily trying to make a point: if working a specific muscle reduced fat in that area, that’s how it should work. But it doesn’t, or doesn’t seem to.
For the most part, the entire idea has been overwhelmingly debunked in the field even if the occasional heretic or book seller suggests it is still possible. A variety of admittedly indirect research argues very strongly against it. For example tennis players show no difference in skinfold measurement between their dominant and non-dominant arm. Despite using the muscles of one arm significantly more, bodyfat is simply not affected.
But these are indirect measurements and, up until this paper, I’m not sure anybody had ever really tested the idea directly. So if something like spot reduction worked, what would it entail? That is, physiologically what would have to occur? Before addressing that, let me give a brief overview of how fat is actually lost.
A Primer on Fat Loss
- Lipolysis (the actual fat breakdown)
- Blood flow (critical for transport of the broken down fat to other tissues for ‘burning’)
- Oxidation (the actual ‘burning’ of fat in tissues such as the liver or skeletal muscle)
So first fat within the fat cell has to be broken down and released into the bloodstream. Then it has to be carried away from the fat cell so that it can be burned somewhere else in the body for energy (i.e. heart or muscle generally).
So the question becomes whether or not local muscular activity could impact on fat cell metabolism in that area in such a way that spot reduction could potentially occur? Perhaps it increases local fat mobilization or blood flow?
In concept, the muscle being worked might use those fatty acids for energy although this is highly unlikely. Skeletal muscle and the fat that sits on top of it are not connected in terms of blood flow. Any fat mobilized from fat cells in a specific area are going to go into the bloodstream with no guarantee that they would be used preferentially by the muscle being worked.
So I’ll only be focusing on the first two steps: lipolysis and blood flow. Which, as it turns out are what the paper I want to examine set out to study: do contractions in a specific muscle impact on either lipolysis or blood flow (oxidation was not measured) in the adjacent fat cells.
Testing Spot Reduction
The study took ten healthy males who performed single leg exercise while lipolysis and blood flow were measured through a couple of fairly technical methods I won’t describe.
Specifically the researchers called it “one-leg leg extension” but this was probably one legged cycling based on the duration. Exercise was performed for 15 minutes at 25%, 120 minutes at 55% and 30 minute at 85% of maximum power output with a 30 minute break between bouts. You can see why I don’t think it was actual leg extensions as no human could do that for 2 straight hours.
The subjects also switched legs every time they changed intensity. This also acted as a control so that the previous bout of exercise wasn’t impacting on the next bout, since the previously exercised leg got the longer break.
By alternating legs this way, the researchers were able to measure and compare lipolysis and blood flow for the exercising vs. non-exercising leg. This is actually critically important as any type of whole body exercise would tend to have systemic effects. That is it would tend to impact on things like blood flow or lipolysis or fuel use all over the body.
By limiting exercise to a single leg, the researchers were able to measure the response only in the fat cells close to the muscles being worked and compare that to the unworked muscle to see what differences occurred.
As mentioned above, blood flow and lipolysis was compared between the exercised leg and the rested leg to see what difference the exercise had.
At both the lowest and highest intensity of exercise (but not the moderate intensity), the researchers found that lipolysis was higher in the exercising vs. non-exercising leg. During low and moderate intensity exercise (but not the high intensity), blood flow was higher in the exercising vs. non-exercising leg.
So this at least suggests that, yes, to some degree local exercise of a muscle increases both blood flow and lipolysis. This would provide at least a potentially plausible mechanism for spot reduction.
But before looking at the specific numbers, we might ask why this happened to begin with. That is, why would the system work this way at all. As I mentioned above, the muscle and the fat that sits on top of it aren’t connected in terms of their blood flow. It’s not as if any fat being mobilized locally can be used by the muscle that is currently working.
So there’s no really logical physiological reason this should happen to begin with. Of course, physiology doesn’t have to be logical to work a certain way. Worrying about the logical “why” of the observation makes it easy to miss what was observed to begin with.
But physiologically why did this occur. The researchers suggest that local changes in hormones (or a synergy between changes in hormones and blood flow) are most likely responsible. Certainly there can be localized hormonal effects and it’s conceivable that local muscular exercise could cause this to occur
They also suggested that a localized increase in temperature might be responsible as this can impact on blood flow. I discuss this aspect of fat cell mobilization in The Stubborn Fat Solution as local temperature is known to impact on blood flow in the area. Cold tends to cause vasoconstriction and heat vasodilation so there might actually be some logic to those rubber belts and such that warm the area before exercise.
In any case, for whatever reasons, through whatever mechanism, working a given muscle for 30 minutes at low to moderate intensities did increase fat cell lipolysis and blood flow in the fat directly above the working muscle.
So Spot Reduction is Possible Then?
So far this study seems to lend at least a plausible mechanism for spot reduction to occur. However, it’s not quite that simple.
First and foremost, the researchers make the important point that these results don’t automatically indicate that localized fat loss will occur. In many cases, fat mobilized from fat cells gets stored right back in those same fat cells, a process called re-esterification. In other situations, fat mobilized from one area gets stored in a different area of the body. As I discussed in The Women’s Book Vol 1, women can store fat in their upper body after a meal and eventually mobilize it and store it in their lower body later.
But there is more important issue here, something you might have noticed I left out above which is the actual quantitative impact of all of this. That is, it’s certainly interesting that local muscular exercise increased local fat cell lipolysis and blood flow. But how much fat was actually mobilized to be potentially burned off of the body.
Based on the measured changes in blood flow and lipolysis, the researchers estimated that, during 30 minutes of one legged exercise, an additional 0.6-2.1 milligrams (one thousandth of a gram) per 100 grams of adipose tissue would was mobilized.
Assuming someone was carrying 5 kg (111. lbs) of fat in a specific area, the calculations would predict the following fat mobilization:
Now one pound of fat (0.45 kg) contains about 450 grams of fat so our hypothetical 5 lbs of fat contains 4,440 grams of fat. And 30 minutes of local muscular activity mobilized at most 0.1 gram. It would take 300 minutes to mobilize a single gram of fat this way. Mobilizing even a single pound of fat would require 136,200 minutes or 2270 hours.
Spot Reduction is Dead
And honestly that should really be it. Despite the people citing this paper left and right, it’s clear that none of them read past the abstract. Yes, absolutely, local muscular exercise in the form of one legged cycling increased local fat mobilization and blood flow.
But the actual impact in a quantitative sense is completely meaningless in the real world. The amount mobilized this way is microscopic and could not meaningfully impact on fat loss in any reasonable time frame.
This is especially true when you compare this type of activity to whole body cardio type exercise. Even at a relatively low intensity, 30 minutes of aerobic activity might burn 5 cal/minute or 150 calories. Someone burning 90% fat during that bout would mobilize and use 15 grams of fat for fuel. Compare that to the 0.1 gram that might be mobilized and burned from 30 minutes of crunches or leg lifts. There is no comparison.
Even if fat mobilization were increased with local muscular activity, the calorie burn would be too insignificant to have a chance of burning them all off. Which does raise the question of whether localized muscular activity prior to whole body aerobic activity might have benefit but that’s another study for another day.
Additionally the whole body aerobic activity will impact on fuel utilization and hormonal response in ways that much more massively impact on lipolysis and blood flow. Simply, doing an hour of localized muscular exercise pales in comparison to an hour of low or moderate intensity aerobic activity in terms of fat mobilized or burned for fuel.