This is a weekly post for the runners of LoseIt. All levels of runners are welcome here. Just ran for the first time, doing C25K (Couch to 5K), or an experienced marathoner – come on in and share, ask questions, or provide advice.
This post is mostly for sharing your weekly progress, first run reports, race reports, asking questions, or running-related NSV (non-scale victories). In addition to this, I ramble on about some topic related to running. This week — the Fat Burning Zone.
Fat Burning Zone and Energy Pathways
I ran into the above article this week and made me think about all the confusing talk about the Fat Burning zone. This is one of those topics that’s important but not because of anything to do with weight loss — instead because it helps you run more easily and improves your health.
So as you move and need/use energy each day, your body has different energy sources it can use. These are – current food generated energy in your bloodstream, adipose/fat stores, glycogen stores, or by breaking lean muscle/tissue. The two key pathways for energy are either from fat or from glycogen stores.
Fat energy or fast energy
The fat fueled energy pathway in your body delivers only so much and only so fast. It’s a slow process that breaks down the adipose fat and turns it into energy. But most of us have a lot of store energy in fat — 3500 calories of it per pound.
Glycogen stores are faster energy, with a wider pathway for energy delivery. Where the fat pathway has you drinking up energy with a straw, glycogen stores allow you to chug directly from the keg.
The Easiest Fat Burning Zone
When you are in the Fat Burning zone you are using energy that is coming directly from adipose/fat being broken down in your body. This level of exercise is very light. Myself, I can get into this zone easily with moderate walking. You don’t need to run to burn fat.
In fact, when you get up in the morning and before you eat you are just burning fat. You are fasted and have no energy from recently eaten food hanging around – so the body used fat stores. This isn’t the zone we are talking about though. Your body using fat stores for the sip-sip-sip of your BMR is not the zone.
The fat burning zone is achieved with exercise, not by couch lounging. The body needs to go looking for more energy than you need being sedentary walking/sitting around the house/workplace.
That Sounds Great, Why Isn’t It Important?
While the Fat Burning zone seems like a fabulous way to burn up calories and tilt CICO towards weight loss — total calories out remain the more important element.
You can fat zone burn for a 60-minute walk and cover 3 miles or 5 km. Depending on your physical stats, you might burn 150-450 calories in that hour. (As a 240 lb 6′ man, I burn about 300 calories on this walk.) Almost all of that will come from fat stores except for any energy from something you just ate.
With that same 60 minutes you can go for a 5+ mile run. Likely this will put you out of the zone and leave you using just 1/3rd your calories from stored fat. During that run you will use close to twice as many calories, maybe 300-900 calories. (I use about 600.) So for me about 200 calories are from fat stores, the rest, 400, are mostly from glycogen stores. Less from fat, but more overall calories out.
Your Metabolism Adapts
Even though you may be out of the fat burning zone for exercise, burning through glycogen instead, your body will ultimately need to get that energy from somewhere. Your body will use carbs you eat to replenish those glycogen stores — instead of storing it as fat.
Now, using energy from fat and from glycogen stores makes your body better at getting to that energy.
If you use the fat burning zone for exercise, you’ll get better at it. If you push that further, say walk more briskly over time. Do slow jog/walk intervals. Your body will get better and better at using fat energy.
If you push into a more glycogen burning zone you’ll get your body to use that pathway better and store more of it.
Theres more than just weight loss
Both of these adaptations are great changes to your body. You can be a better fat burner. Able to slowly run using mostly fat stored energy — as keto adapted runners do. With more vigorous exercise you can also make your body sock away gylcogen more readily instead of storing it as fat.
The more you exercise in the fat burning or glycogen burning zones, the better. You are getting your body used to using food you eat to go other places than fat or BMR. It is a energy spending machine, instead of an energy storing one.
These adaptations are incredibly useful in fitness but also in your health. These same processes help keep diabetes and heart disease away.
How did your week go? Get your miles in? Finish a week of C25K? Training for a virtual race or some goal? Let us know!
Also if you have any questions – ask away.