Does Your Body Have to Be In Ketosis to Burn Fat?

June 1, 2005 5:06 PM

Does a normal body have to be in ketosis to burn fat? If your body is not producing ketones, does that mean that your body is not burning fat?
posted by Dr. Zira to health & fitness (9 comments total)

No, ketosis is only when your body runs out of glucose to power your brain. You burn fat every night, when your liver makes glucose to power your brain, and the rest of your body uses fatty acids (from fat) to keep the rest of your body going.
posted by gramcracker at 5:15 PM on June 1, 2005

No. You burn fat all the time.
posted by grouse at 5:18 PM on June 1, 2005

No, you burn fat all the time. It's our primary reserve/storage for energy. Ketosis only happens when you are running low on carbohydrates. "Fats burn in the flame of carbohydrates." Ketosis isn't good and makes the blood acidic. That being said, I think 3/4 of the brain's needs can met by ketone bodies during starvation. Wow, my biochem class paid off!

On preview, what g & g both said.
posted by keep the aspidistra flying at 5:26 PM on June 1, 2005

Let me join the chorus: No, you burn fat all the time.
posted by jdroth at 5:57 PM on June 1, 2005

A normal body in ketosis is burning a large percentage of muscle mass (protein) and a small amount of fat. Fat burns much more effectively when burned with glycose/glucogen...

When you lose weight in ketosis it's because you're losing a lot of water weight & muscle mass. Muscle mass is not what you want to be losing. They're heavier than fat, but oh so much more useful in so many ways.
posted by susanbeeswax at 9:10 PM on June 1, 2005

No.

When you use more calories than you are eating, the body breaks down fat from the adipose tissue into glucose via the Krebs cycle. When fat oxidation is too fast for the liver to break down the acetyl-CoA, ketones are the result and are a useful source of energy for extra-hepatic tissues (including brain) during starvation.

Much more information can be found here.
posted by aaronh at 6:36 AM on June 2, 2005

I've gained weight a couple of times by massive weightlifting for a few months. When I've stopped, eventually all the gains have vanished, sometimes over just a couple of days. Unfortunately, I've also picked up a small gut which doesn't seem to vanish no matter what. Although I notice it diminishes somewhat if I miss a meal or two. Any thoughts on why? Especially not being able to hold onto muscle mass? Should I post this as its own question?
posted by atchafalaya at 7:02 AM on June 2, 2005

Yay. I can throw away the ketostix then and focus on eating good carbs. I never really did Atkins, but last summer I cut sugar and refined flour out of my diet and lost about 25lbs. While I appreciated the results, I was in ketosis most of the time, and felt like crap in ketosis. This time around I'd like to move more toward a low-fat, whole-grain diet and stay out of ketosis.

Because I stopped regular workouts for a few months, I've gained a couple of pounds. Now that I have more free time for the summer, I just started workouts again in hopes of trimming up. Like atchafalaya, I've picked up a bit of a gut which I'd like to lose and would love to hear any answers to that question as well...
posted by Dr. Zira at 10:35 AM on June 2, 2005

While I never had big gut, I have had a rather floppy midsection at times when I have cut out exercise and cut in copious booze and other items. While I believe the general idea that there is no such thing as "spot reduction" I found that good cardio (hill-walking) combined with a lot of trunk exercise (at least a total of 500 crunches in a variety of forms and 100 push-ups, each in sets of 25) every day got my upperbody into the good shape. Unfortunately it took about 2-4 hours out of the day. I haven't been suffciently underemployed to do that in a while, but three months of that trims me down and then that regime cut approximately in half usually keeps me in whatever shape I find myself. I am sure there are many reasons why this is ineffecient or non-ideal or whatever, but the daily routine made it very difficult to "cheat" the schedule. It became like brushing my teeth.
posted by mzurer at 11:59 AM on June 2, 2005