T Nation

Insulin and Cardio


My question is this:

How long do carbohydrates roughly cause an insulin spike and does that insulin spike make it impossible (or harder) to burn fat while doing cardio?

Or to put it another way, how long after having eaten post-workout starchy carbs do I have to wait so that cardio will burn as much fat as possible?


If I were you I'd keep my cardio days from weight days.Latley I've been learning some interesting stuff at my college. Insulin spikes don't really cause you to store fat.It's only when fat is present that you'll store fat.Don't focus on the technical jargon in the next paragraph, just try to grasp the overall point. You don't need to be a scientist to use common sense and basic reasoning skills. Ready?

Consider this bit of biochemistry. Malonyl -CoA exists in high amounts when there is plenty of metabolic fuel present. Thus, carnitine acyltransferase is inhibited and
this in turn prevents acyl-CoA from crossing into the cell?s mitochondria. Another enzyme is inhibited by the presence of NADH and Thiolase is also inhibited by the presence of Acetyl-COA. In short, when a lot of glucose is present, fatty acid metabolism is inhibited.

It is the last sentence that clues us in here. Basically, a cell will not convert fats into energy if there is glucose present. When the cell has carbs and sugar to work on, it will not convert the fat to energy, thus the fat gets stored.

This is why the low carb diets work, with little to zero carbohydrates and
subsequently glucose to work on, the fat will be used for energy. This is exactly why the high carb diet works too. When no or little fat is present, it won't be stored as fat.

In addition to this, it is important to realize that it costs the body quite a bit of energy to take carbs and store them as fat. This alone is actually a positive. There really needs to be some form of fat present to make it easier.
Both diets make you lose weight,but carb diets work a bit faster.Why? Because every gram of carbohydrate consumed causes the body to hold 2.4 grams of water.Thats why a huge part of the weight on those low carb diets that you lose is usually water,then muscle.Then there is ketosis where the body relies on stored muscle tissue for energy. You see,the last thing the body wants to use up is it's fat stores.Thats the last thing the body wants.It would rather use muscle tissue first. If you're lifting 3-4 times a week and trying to gain muscle I'd tell you to limit the cardio.Some people say to wait SEVEN hours before doing cardio(after lifting weights).When you do do cardio,keep it low impact. meaning you should be able to talk while doing so.If you're huffing and puffing you could be breaking down muscle tissue. So,if you do do cardio before breakfast,make sure it's low impact. Now,for as having carbs before doing cardio? Sure. Calories coming from glycogen stores and fat are two different things. When you lift weights you usually burn off carbs/sugar,unless you did cardio before hand.If you have some carbohydrates and do some cardio you'll be able to burn fat.Just keep your heart at a consistent beat. Don't stop,or slow down,or go faster.Keep it low impact and you'll burn fat.This works great for me.


Thank you for the reply, however that was not quite what I?m looking for.

My reaction to carbohydrates is very strong. If I concentrate C+P around my workouts in the morning I will not loose muscle while dieting.

My problem is my lack of knowledge of the fat metabolism. Is it possible for the human body to get to the energy stored in fat cells while insuline levels are high?

If it is not possible or harder, how long after a C+P meal would I have to wait until I have similar conditions like I would have in the morning pre-breakfast (fasted cardio)?


As I understand it, glucagon and insulin are pretty much mutually exclusive; that is, once you start exercising, insulin production is lowered as glucagon production is increased. In essence, storing stuff is put on hold in order to use stuff.

That obviously doesn't account for fat metabolism, but basically your concern isn't really a problem, as when you start to do aerobic exercise, insulin levels go down the crapper anyway.

Reaper has a point about there being glucose present in your muscles, though, even after a weight training bout. Even intense lifting leaves about 40% of glycogen hangin' around.
One theorized reason is that muscles simply don't get a chance to use everything before muscle function is shut down (the two most probable mechanisms are hydrogen ion accumulation around DHPR and/or potassium accumulation outside the cell). In any case, carbohydrates will be used preferentially during long duration training while fat is generally used in non-contractile processes while there are enough enzymes floating around to utilize carbohydrates in aerobic respiration. Once those enzymes are used up/to capacity, fat and protein tend to be used in reasonably equal portions to provide energy during long-duration activity.

The take home message is that building more lean mass and creating the largest EPOC possible through weight training are much more efficient at burning fat than endurance training. That's two of the reasons Tabata training works so damn well.

Oh, side note to reaper - low impact does not refer to intensity, but rather stress put on joints during activity. "Moderate intensity" is the term you were going for with being able to talk while exercising. Light intensity is being able to basically sing, while high intensity is difficult to get a few words out at a time.



Lol,yeah,you know what I mean though.