Sunday, August 15, 2010

Nutrition ABCs: Calories

There were a lot of ways to go with the letter carrots, carbohydrates or calcium....but I thought that it might be a nice idea to really get back to basics and talk calories. Calories are top of the list on the nutrition facts panels, so they must be important right? We count calories when we are watching our weight, we burn calories through activity and food manufacturers market their 100 calorie snacks as being better for us than those with larger (and less round) numbers. 

We talk calories every what exactly is a calorie and why does the amount of calories we eat matter? 

Here is the scientific version -

A calorie is a unit of heat energy: to be accurate, what we call a calorie in nutrition speak is actually a kilocalorie, or 1000 calories of heat energy. To simplify, we won't concern ourselves with that technicality but say that one calorie is the amount of energy in the form of heat it takes to raise the temperature of one gram of water by one degree Celsius. Huh? 

What this definition illustrates most importantly is that a calorie is not just a made up concept (which is a question I have been asked yes, Virginia, a calorie is a real thing!). 

When a food has 250 calories, for example, it means that it can provide your body with 250 units of energy once it is digested and absorbed. To learn how many calories are in a food, the food is actually burned in a lab in a device called a bomb calorimeter to determine how much energy it gives off. A simpler way of doing this is to calculate the calories based on known values for the ingredients (but all data had to come from somewhere...burn baby burn!).

While food provides energy, our body spends it keeping us alive: from breathing to digesting, talking to walking, each function and activity we carry out requires energy and the food we eat provides it. Think of it like a living bank account: if our bills and expenditures keep draining the account and we put nothing in it, we are going to bounce our checks and soon our phone will be turned off and we will lose our homes. 

Our best research based equations to determine how much energy we need in a given day are not really that accurate and can over or underestimate by 10 - 30%. The best way of measuring how much energy a person needs is to actually contain them within a hood and measure their respiration on something called a metabolic cart. By measuring the use of oxygen and release of carbon dioxide, we can measure the energy that a person requires to maintain life. However, most of us will not get the opportunity to try out this process; the best way to know if we are doing well is to determine whether our weight is stable. If it is, we are doing a good job of maintaining energy balance: the calories in roughly equal the calories going out.

If we were to eat nothing or deprive our bodies of adequate energy for long periods of time, we end up with an energy deficit and our bodies go into conservation mode. Doing so moderately is how we lose weight...long term or severe deprivation wreaks havoc on our optimal metabolic state and affects everything from our energy levels to our immune system to our strength and mental function. And our bodies are smart: let your calorie intake drop too drastically and your body will respond in kind by lowering its rate of metabolism, meaning that you will need fewer calories just to maintain your weight...which is how chronic dieting can get you into trouble and encourage weight gain long term.

Our body stores energy mainly in fat cells: one pound of fat tissue stores 3500 calories of energy. So to lose a pound, we have to create a deficit of about 3500 calories, which most health professionals would counsel you should do over about 4-7 days for a healthy, moderate loss of one to two pounds a week. To gain a pound, you need to consume about 3500 calories more than you need, which seems like it would be tough to do but it sure can sneak up. Here is a great example -

Say you go out to Starbucks and get a regular coffee Frappucino because it is a hot summer day. You don't go crazy and get whipped cream or a large size and so your treat sets you back about 140 calories. That seems pretty reasonable, doesn't it? But let's say that you drink that Frappucino in addition to your regular don't eat less during the day or exercise more to compensate. And say that you enjoyed that Frappucino so much that you decide to get one the next day and the day after that and continue to do so for one year. Over that year, you would have eaten 51,100 extra calories. And if your body is efficient and turned each 3500 calories into a pound of fat, you would have the potential to have gained 14.6 pounds. All by having a Frappucino a day. The upside to this equation is that the reverse is true: take that drink out of your daily routine and you can lose weight without making any major changes to your diet.

So where does the energy (or calories) in a food come from? From the macronutrients they contain: carbohydrates, fats, protein and alcohol. Water, vitamins and minerals while essential for life do not provide energy (so they don't contain calories). Fat contains 9 calories per gram and is the richest source of energy. Carbohydrates and protein both provide 4 calories per gram and alcohol rings in at about 7 calories per gram. When people say that fat is fattening, it is not because it has any special evil powers but it is easy to get more energy than you need when it is more than double the energy, gram for gram, over carbohydrate or protein foods. 

It can be easy to make the mistake that all that matters when it comes to health or weight is calories - and many health professionals fall into this trap too. Note the low fat fiasco of the 1990's in which we switched to tons of processed fat free carbohydrate snacks and got fatter than ever. While calories provide energy and ensuring a good energy balance is important for a healthy weight, calories tell you nothing about the nutritional value of a food: the nutrients it provides, the way it affects your blood sugar or how satisfying or filling it is.

So why do calories matter? My number one rule of healthy eating is to generally eat whole foods without fancy packages...fruits, vegetables, whole unprocessed grains, lean proteins and dairy (or non-dairy). If you follow this rule, it is unlikely you will need to count calories to maintain a healthy weight (and note that many of these foods don't even have nutrition facts panels!). However, if you are looking at processed foods like cereals, snacks or most importantly, fast food and restaurant foods - you can use the calories to compare a better choice.

Hmm...this post could easily go on and on so I might stop there....but first I'll give you the Coles Notes version:

- A calorie is a scientific unit of heat energy used to measure the energy that foods give you or that human activities consume.
- The calories in food come from fat, protein, carbohydrates or alcohol...not from water, vitamins or minerals.
- Calories are important because if we consume more energy than we spend, we will end up gaining weight.
- Calories will not, however, tell you anything about the nutritional quality of the food which has a bigger impact on your overall health (provided you are not gaining weight).

if you have any other questions, let me know and I will address them in an update!

In good health,

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