Im really excited about today’s guest post.
Not only am I a bigbig fan of Darya’s blog —-I love and admire her ability to explain science in a clear, concise & *understandable* fashion.
Thanks so much Darya for making time to explain what I totally could not respond to a MizFit reader comment.
EDITED TO SAY: The initial post can be found here.
• Anne Keckler | ACSM Certified Personal Trainer Says:
March 24th, 2009 at 9:32 am
The cleaner you eat the more calories you can consume while not gaining weight.
I’d like to have a scientific explanation of this.
I just want to start by saying, I LOVE a skeptical reader. Kudos to Anne for requesting facts to support this unconventional wisdom offered by MizFit.
While it seems pretty safe (and within the laws of thermodynamics) to say that a calorie is a calorie, and that “calories in must equal calories out,” this is actually an oversimplification of the way our bodies work.
To put it simply, a calorie IS a calorie, but how your body uses that calorie is dependent on context. In other words, the way those calories are delivered to you (i.e., the food you eat) can affect how your body metabolizes them.
There are three ways your body can deal with a calorie. It can use it immediately, it can store it, or it can skip digestion and let it go untouched. Fiber is a good example of something you cannot digest. Any calories locked in fiber (not calories surrounded by fiber, but the fiber itself) will not contribute to your metabolism.
When we talk about “using” a calorie, most of the time we are referring to burning glucose as fuel in muscle tissue. When we “store” a calorie, it means the glucose (sugar) was converted to fat and placed in special tissue called adipose.
But what determines whether we use or store a calorie?
Under normal circumstances this decision is made in the blood. When you digest food that contains calories, your gastrointestinal system converts the carbohydrates you have eaten into blood glucose. It turns out that how quickly this happens is extremely important for how your body deals with those calories.
Most of us would prefer that all the calories we eat go directly to muscle fueling and not to fat storage. Better muscle fueling causes us to burn more calories involuntarily—this is your “metabolism.” What and when we eat determines how effectively we fuel our muscles. Any extra glucose that is not burned is converted to fat and stored.
Glucose can only enter (fuel) your muscles in the presence of a hormone called insulin. Insulin is produced by your pancreas in response to high blood sugar (i.e., after a meal). But your muscles can only detect insulin if they have insulin receptors. Think of insulin receptors as the lock and insulin as the key to let glucose into your muscle tissue. How much glucose can get in at one time depends on the size of the door.
The scientific term to describe the size of the door is insulin sensitivity.
Your body tries its best to maintain stable blood glucose and insulin, so when there is a rush of blood sugar it is in a hurry to get it out of the blood ASAP. If glucose cannot get into muscles fast enough (option #1), it is whisked away into fat (option #2) to return levels to normal.
We all have a set level of insulin sensitivity right now. The more insulin sensitive you are, the more glucose can fuel your muscles at one time. But if you are insulin resistant, your insulin door is easily jammed up with extra glucose. This causes the calories that would have been burned as fuel to be stored as fat.
But it is important to remember that no matter how insulin sensitive you are too much glucose at the same time can overload your muscles and cause extra calories to be diverted from your muscles to fat. You do not have to be insulin resistant to force fat storage.
Conversely, if you stretch out the same amount of glucose and insulin over a longer time period (a long, slow peak rather than a spike) those same calories can be burned as fuel in your muscles instead of being stored. This is equivalent to glucose getting in a single file line to fit through the door rather than trying to force its way in like an angry mob.
To summarize, a calorie is not a calorie when you have a blood glucose and insulin spike that forces it to be stored as fat rather than used as fuel.
What causes a blood glucose spike is a meal loaded with quickly digesting carbohydrates. These foods are very rare in nature, but are abundant in our Western culture and are called processed or refined carbohydrates.
Another nutrient that can negatively impact your insulin sensitivity is saturated fat.
When Miz says she tries to eat “clean” food, it is less processed and therefore less likely to cause a blood sugar spike. Based on her daily diet, she doesn’t eat much saturated fat either.
If your muscles are stressed too often with excess blood sugar the number of insulin receptors will decrease, your glucose door will shrink, and you will become more insulin resistant. This has both short and long-term effects. Spiking your blood sugar at breakfast will make you more insulin resistant at lunch. Stretch this over years and you develop type 2 diabetes.
If that does not scare you enough, insulin signaling is also strongly linked to more rapid aging. So not only do blood sugar spikes make you fat and give you diabetes (and probably heart disease), they are making you older too.
Fortunately, the vast majority of delicious foods on this earth do not promote blood sugar spikes. You can eat all the vegetables you want (fruits are a little sweeter, but still very good for you). Whole, intact grains take so long to digest that they beautifully distribute your blood glucose peak over several hours, helping you avoid a glucose spike while providing perfect muscle fuel. Lean meats like fish and poultry have almost no impact on blood sugar and contain little saturated fat.
Finally, what you eat can also contribute to the number of calories you want to eat. A well-fueled, nourished body does not crave sugary, processed foods because it already has what it needs.
If you are eating a variety of whole, mostly plant-based foods, the calories you eat are very different from the ones you would get from junk food. This is not because of the calories themselves, but because of how your body deals with them.
Darya is a scientist, San Francisco foodie and advocate of local, seasonal foods. Summer Tomato offers tips and advice on healthy eating, especially for foodies in urban areas.