If you follow health news, you might be thinking exercise doesn’t matter when you’re trying to lose weight. Vox just published  a big piece showing how useless exercise alone is for weight loss. The NY Times says  “eating less” is way more effective than “exercising more.” Obesity researchers like Gary Taubes and Yoni Freedhoff—who don’t agree on much else—both think  using exercise to fix obesity is futile . I’ve always said that 80% of your body composition is determined by your diet, not how you exercise. And everyone knows it’s really hard, bordering on impossible, to out exercise a bad diet. You might be able to out exercise a bad diet if all you care about is abs and race times and make it your job, but eventually your poor health will catch up with you.
That doesn’t mean exercise doesn’t matter for weight loss, though. It does.
What is true? The value of exercise doesn’t depend on its caloric burn. The studies cited in the media pieces make it clear that energy expenditure through exercise has very little effect on weight loss. To focus on that and discard the effectiveness of exercise in general is misleading, though. And wrong, because fat loss isn’t just about mechanistically burning calories.
Notice what I wrote: fat loss.
We’re not trying to burn bone, or dissolve muscle, or shave a few pounds off our internal organs . All those things will reduce your weight but also your health, performance, and lifespan. We’re trying to burn fat. To take a couple notches off the belt. To look good naked . That’s what nearly everyone means when they say “lose weight.” So even if exercise doesn’t lead to a significant net loss of weight on its own, it can help us preferentially remove body fat while retaining lean mass.
So let’s see how exercise can help weight loss, both directly and indirectly. By the end of today’s post, you’ll be itching to go lift something or run really fast up a hill.
Exercise empties glycogen
If your glycogen  stores are full, any extra carbs that aren’t immediately burned for energy will be shunted to your liver for conversion into fat, aka de novo lipogenesis. If you exercise hard enough to empty those glycogen stores, you’ve just cleared space for the carbs you eat. They’ll refill glycogen stores. Conversion into glycogen is a desirable metabolic fate for carbs. Carbs locked into muscle glycogen stores will not contribute toward fat stores. Instead, they’ll contribute toward high-intensity physical activity that aids fat loss.
One study  found that depleting glycogen stores with exercise reduced postprandial de novo lipogenesis in subjects fed a carb-rich meal. Compared to the non-exercising control group, the exercisers experienced three-fold higher postprandial muscle glycogen synthesis (more dietary glucose became muscle glycogen) and a 40% reduction in hepatic triglyceride synthesis (less liver fat produced).
Exercise improves blood glucose control
Although the scientific community debates the etiology of “hangry,” I think it usually stems from reactive hypoglycemia. Consider the sugar-burner whose blood sugar spikes after a meal then drops lower than it was before the meal. He won’t be able to access body fat for energy. His body wants the only kind of energy it knows—sugar—and it’s just not there. He’s going to eat something sugary and right away.
Now consider the fat-burning beast  with low blood sugar. Is he going to freak out and binge because no energy’s available, or does he have the metabolic machinery necessary to take advantage of all that animal fat hanging around?
Who’s hungrier? Who eats more? Who gains more weight?
Smart exercise can help you establish better control over your blood glucose levels. It doesn’t take much, and most modalities work: moderate resistance training , moderate endurance training , both uphill and downhill walking , walking , walking meditation , sprinting .
The best type of exercise that improves blood glucose control without inducing hypoglycemia in its own right is probably low-rep, high-weight strength training, walking, and short sprints (and I mean really short, like 5-8 second bursts).
Exercise improves sleep
Sleep  is where fat loss actually occurs, because when you sleep, you experience the biggest spike in fat-mobilizing growth hormone. When you don’t sleep, cortisol increases to compensate for the groggy headspace and muddy thinking. Chronic levels of stress hormones, from chronic bad sleep, lead to fat retention, especially in the belly.
Strength training  and aerobic training  all help sleep (sprinting should as well, but I wasn’t able to find any solid evidence in either direction). Put nursing home seniors on an elastic band training program and you’ll improve their sleep . Put hard-headed obese teens on an exercise program and they’ll start sleeping better and longer . Exercise even improves  depression-related sleep disturbances and mitigates muscle loss caused by sleep deprivation . It’s not magic, but it’s close.
When you exercise can affect your sleep negatively, of course. Don’t train at 11 PM in a fluorescent light-lit gym  with blaring pop music. Don’t settle for 5 hours a night because you want to wake up at 5:30 for a workout.
Exercise beiges white fat
What are those words you just wrote, Sisson? “Beige” isn’t a verb.
You all know about brown fat, the metabolically-active genre of body fat that burns calories to keep mammals warm in cold temperatures. It increases energy expenditure and the fatter you are, the less brown fat you have and the less metabolic activity you show in the brown fat you do have . Brown fat is awesome stuff and almost certainly makes it easier to lose fat.
One cool thing about certain types of exercise is that it can make white adipose tissue behave more like brown adipose tissue . Hence, “beige.” It does this by reducing the size of fat cells, reducing the lipid content of said fat cells, and building more energy-consuming-and-ATP-producing mitochondria  within the fat. Transplanting exercise-induced beige fat cells into sedentary controls improves their body-wide metabolic homeostasis and increases their muscles’ uptake of glycogen. This beigeing of white fat improves body-wide metabolic homeostasis and increases the uptake of glycogen by your muscles. It helps nutrients go where they’re useful.
(To make sure your exercise is working, remove a dime-sized pat of butt fat with a grapefruit spoon and observe the color. If it’s beige, you’re on the right track!)
(Please disregard the previous parenthetical.)
Exercise increases our resistance to stress
People respond to stress in many different ways. Some stay awake at night, endlessly ruminating on the hundreds of outstanding responsibilities. Some freeze up, unable to progress. Some go hungry, refusing even their typical favorite foods. But perhaps the most common response to psychosocial stress is binge eating junk food (PDF ). This is especially common among women (PDF ), who tend to focus on salty, sweet, and fatty snack foods. Stress eating is a major risk factor  for weight gain; anything that reduces stress will probably increase fat loss.
Exercise blunts our stress response . When we’re physically fit, or we’ve just come off a tough 30 minute lifting session, stressors that’d fell a sedentary person just roll off the back. Training doesn’t just make our muscles stronger and our cardiovascular system more efficient. It trains our psyche, too.
Exercise makes movement fun again
It won’t always do this. But in my experience, when people get fitter, stronger, faster, and more confident in their own bodies, they enjoy their own bodies again. They start moving for the sake of moving. They’ll go for hikes  because they enjoy it, not because they’re trying to work out. They’ll play sports  again, and start walking when they would have driven. Movement becomes an integral part of their lifestyle. And once non-exercise activity thermogenesis—energy expenditure through daily movement, not formal exercise—increases, fat loss often follows.
Exercise increases your calorie sink
Exercise gives you a little wiggle room. It lets you eat enough to be satiated. It allows you to eat enough food to get the micronutrients you need. A full-on calorie restriction weight loss diet without exercise is rough; you must micromanage your entire day just to ensure you’re obtaining the vitamins and minerals your body needs while battling constant hunger. When you throw in exercise, you can eat a bit more. You don’t have to plug everything into a nutrition calculator. You can have an extra helping of potatoes to get more potassium, resistant starch, and magnesium. You can add another half cup of full fat yogurt with a blueberries to get your calcium and phytonutrients. Fat loss diets get easier when you train.
“Exercise” doesn’t tell us much, of course. There are many ways to exercise, and some are better than others for improving body composition and burning fat.
Much has been made of the studies  showing that people training for a marathon fail to improve body comp. Over the course of 18 months of hardcore marathon training, males lost just 2.4 kg of fat and women didn’t lose any. That’s 18 months of pounding the pavement, and weight barely budged (and not at all in women). Everyone knows by now that endurance training isn’t great for body comp.
The overall most effective way for your average overweight to obese person starting from square one to lose fat and retain lean mass is resistance training combined with a low-carb Primal way of eating.
A recent study  found that the most effective method for weight loss in the severely obese was diet+resistance training. Compared to endurance training+diet or endurance training combined with resistance training+diet, simply focusing on strength training and diet produced the best results for the severely obese. The most effective kind of strength training was whole body exercises using free weights. There was some evidence that if you wanted to add “cardio” training to your lifting, high-intensity interval training/sprinting was the only one that really worked. Typical endurance training was ineffective. This makes sense. It’s high-acute stress (your workouts are really tough but end quickly) and low-chronic stress (which few people, least of all sedentary obese people, are equipped to handle).
For people who are close to their ideal body composition but want to shed the last 10-12 pounds of body fat, sprinting has to be considered. This is the simplest (yet most intense) way to lean out those last few pounds.
For everyone else: lift, walk lots, and sprint if you’re able.
But honestly? Almost everything works. No matter what exercise modality you study, they’ll all generally improve your metabolic health, increase your muscles’ capacity for glycogen, increase your strength, improve whole-body glucose control, help you sleep better, and make your body fat a little more metabolically active. They can easily get out of hand—I’m looking at you, endurance athletes, 5-6x weekly CrossFitters—but nothing has to.
Combine your exercise with a Primal way of eating and you’ll be on your way to easy, sustainable fat loss. I’m biased, of course, but for good reason: this stuff works. A recent study  of the paleo diet in middle aged type 2 diabetics found that while diet alone works (especially if it’s something like paleo) really well, it works even better when you throw in some exercise.
Over the course of 12 weeks, paleo diet-only subjects told to follow standard exercise recommendations (moderate cardio for 45 minutes to an hour three times a week) lost 5.7 kilos of body fat. Those who participated in supervised aerobic and resistance exercise lost 6.7 kilos.
Diet-only subjects lost 2.6 kg of lean mass, paleo exercisers only lost 1.2 kg of lean mass.
Leptin, the pro-metabolism hormone that increases satiety and energy expenditure, dropped by 62% in the diet-only group. In the exercisers, leptin only dropped by 42%. Higher leptin means higher energy expenditure and lower appetite—both important for weight loss.
All in all, paleo dieters who exercised lost more body fat, retained more muscle, and had stronger metabolisms than those who didn’t. Sounds familiar, eh?
To sum up, training and diet work synergistically. You need both, and stalls in weight loss can often be countered by doing whichever one you aren’t. For most of you reading this, you’ve got the diet down pat. You’re eating well, you’re monitoring what you consume. But you might not be training. Today, right now, that stops. You have the tools you train effectively. You have the justification to train. You now know how imperative it is for your health, your performance, and, yes, your body fat levels that you move your body consistently.
Directly using exercise to incinerate calories and shift your energy balance isn’t sustainable. Eventually, you’ll burn out, or start bingeing on junk, or the health consequences will surpass the benefits.
Using smart exercise—lifting heavy things, running really fast once in awhile, running longer distances without lapsing into chronic cardio,walking, hiking, biking, climbing, playing, and generally just moving—to supplement a healthy diet is the only way to do it.
If exercise aids fat loss, it does so indirectly. It builds lean mass that consumes more energy and perpetuates more exercise. It clears glycogen stores, ensuring the carbs you do eat go to a good cause. It improves blood sugar control, limiting the peaks and valleys that cause many people to snack. It improves your mental health, self-confidence, and resistance to stress, deterring the types of destructive, depressive behaviors that often lead to binging and gorging and weight gain. It even seems to improve our sleep habits.
But it still does it.
What do you think, folks? What’s been your experience with exercise as a tool for fat loss? Has it worked? Has it not? Let me know down below!
Thanks for reading.
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