Metabolism Confusion

A lot of the questions my students are asking have to do with metabolism. Unfortunately, most of them are also based on faulty assumptions and myths. In this post, I am going to try to clear some of these up.

One of the questions I received was: Why is it harder for some people to lose weight and easier for others? This is a common question that many people have, whether or not they verbalize it. When people talk about metaobolism, I think they are referring to some genetic, unchangeable characteristic that determines how quickly your body uses energy; something similar to eye color or shoe size. While there may be some genes having to do with the way fat is stored and used(which are beyond the scope of my knowledge), I believe that MOST of the differences in ability to lose weight between people do not have anything to do with the rate at which calories are burned. Here's what does matter:

- Weight: Believe it or not, the heavier you are, the more calories you burn! Why? Because you have more cells that need those calories. It's simple mathematics. If you drive 2 cars, you need twice as much gas as you would if you drove 1 car the same distance. Similarly, if you have 2,000 fat cells, those cells require twice as many calories as 1,000 cells.

- Muscle mass: Like weight in general, muscle needs calories to exist. But, muscle needs more calories than fat cells, so someone who gains 10 lbs of muscle will burn more calories than someone who gains 10 lbs of fat. This is also why men tend to lose weight more easily than women. They have more testosterone, and therefore more muscle, which means they burn more calories.

- Age: Although calorie needs do decrease with age, it is primarily the result of other changes which can be avoided. As we get older we tend to be less active, which of course will decrease the calories we burn. Furthermore, inactivity will decrease our muscle mass, which will also lead to reduced calorie needs. Changes in hormones also tend to make it more difficult to maintain muscle. But it does not have to be this way. The simple way to combat this is to be more [hysically active and work at building muscle with resistance exercise.

- Height: This is related to weight. It is unfair and unfortunately, not something we can change. Because a healthy BMI is based on a weight-to-height ratio, taller people are supposed to be heavier. It makes sense. Two hundred pounds would look very different on a 7 foot tall person than someone who is only 5 feet tall. Plus, taller people also have more bones and other tissues which all need energy. So, if you are tall- lucky you! You get to eat more calories and still maintain a healthy weight. If you are short- well, you just aren't so lucky. You can't eat the same amount as your taller peers and get away with it.

These factors will affect how many calories your body needs on a day-to-day basis. But there are other things that will affect your calorie balance (calories in vs. calories out). They are pretty obvious:

- How much you eat: Although some of those "fast metabolism" braggarts may swear that they eat fast food five times a day, I am skeptical of these claims. It may be that the people who are "naturally thin" or who lose weight easily are simply not eating that much. They may think they are eating more calories than they actually are. And what about those painfully thin celebrities who credit their metabolisms for their slim figures? It's BULLSHIT plain and simple. They just don't want to admit they are anorexic/bulimic/cokeheads/etc.


- How physically active you are: Again, even non-exercisers may be more active than they think. Research has shown that some people can fidget away extra calories unconsciously. So, people who think they have a fast metabolism may just be fidgeters.

Finally, fat distribution can also play a role in how easy it is for a person to lose weight. Fat that is stored in the lower body (hips, butt, thighs) is harder to lose, whereas fat stored in the abdomen is mobilized more quickly. But, the flip side of this is that lower body fat is much less dangerous to your health (and less unsightly, in my opinion) than upper body fat. This is another reason why men tend to lose weight faster than women. They tend to store more upper body fat.

So, if you want to give your metabolism a boost, forget about weight loss drugs and try muscle-building exercise!

Small, frequent meals vs. 3 squares a day

I have just discovered a new trove of blog topic material: the students in the nutrition class that I TA. The class's instructor requested that the TA's collect a nutrition-related question for each student, to help guide her lectures. But I think that a lot of their questions are probably the same questions that a lot of people have. But most people don't ever take a college nutrition course to learn the answers. So, I've decided to try to answer some of their questions (and maybe yours, too).

First up: Is it better to eat 3 meals per day or more frequent, smaller meals?

When I was an undergrad what feels like millenia ago, I thought I knew the answer to this. My then-boyfriend and now-husband used to think that the anonymous posters on internet bodybuilding forums were the best source of information about this kind of thing. And according to BigGuns123 and SwoleDude456, it was a no-brainer: 6 small meals per day was best for gaining muscle and losing fat. Period.

WARNING: Science-y stuff ahead. Skip this section if you are easily bored
Their argument was that after 3 hours of not eating, the body would start to break down muscle (they even used the word "catabolize" so they'd sound smarter), which ultimately leads to a decrease in metabolism. Also, the process of digestion itself was supposed to boost metabolism. I have some serious doubts about these theories. It is true that some calories are burned during digestion, but I don't see any reason to believe that the body would burn more calories digesting 300 calories 5 times than it would digesting 500 calories 3 times. The energy that is used during the breakdown of nutrients is the result of the way the chemical bonds in those nutrients are broken. So, the amount of energy needed for digestion during any given day should be dependent on the amount and type of nutrients consumed, not how often they are consumed. Second, although I am not an expert on metabolism, I am pretty confident that muscle breakdown does not occur to a great extent until fasting has been prolonged. Instead, during at least the initial 4 hours after a meal (1), the body's stores of glucose (glycogen) are used for energy along with fatty acids (from, you guessed it.. fat). Even when muscle is broken down for energy, this would only result in a net loss of muscle if protein intake throughout the day was not sufficient to replace it.

The other, more logical, argument for small frequent meals is this: if you eat regularly, you will not get a chance to feel very hungry. And when you're not ravenous, it's much easier to make smart choices about what you're going to eat and to stop eating when you are full. On the other hand, when you come to the table starving, you will eat whatever you can get your hands on and you will eat much more than your body actually needs.

Regardless of the bases for these theories, they are still just theories. What's important is what actually happens. What evidence is there to support them? As it turns out, this question does not have an easy answer. One study found that children who eat more meals are less likely to be overweight.(2) Eating just one meal per day appears to have negative effects on cholesterol and blood glucose.(3,4,5)However, there doesn't appear to be much research comparing 3 meals per day to 5 or 6 meals per day. So, it is difficult to determine whether one pattern is better than the other.

Here's my stance: Don't eat by the clock. Eat when you are hungry but not starving, and stop eating when you are comfortably full. If you feel hungry 3 times per day, then eat 3 meals. If you feel hungry 6 times per day, eat 6 meals. As always, the total calories you consume matter much more than when or how you consume them. So, eat in a way that will help you to not eat too many calories. If you are prone to snacking mindlessly all day, you may be better off limiting your eating to 3 main meals only. However, if you are more likely to stuff yourself silly at every meal, you may benefit from having smaller, more frequent meals that keep you satisfied all day so you are not driven to overeat.

References
1. Morton, The Digestive System, 2001
2. Toschke AM, Küchenhoff H, Koletzko B, von Kries R. Obes Res. Meal frequency and childhood obesity. 2005 Nov;13(11):1932-8.
3. Stote KS, Baer DJ, Spears K,et al. A controlled trial of reduced meal frequency without caloric restriction in healthy, normal-weight, middle-aged adults. Am J Clin Nutr. 2007 Apr;85(4):981-8.
4. Bhutani S, Varady KA. Nibbling versus feasting: which meal pattern is better for heart disease prevention? Nutr Rev. 2009 Oct;67(10):591-8.
5. Carlson O, Martin B, Stote KS, et al. Impact of reduced meal frequency without caloric restriction on glucose regulation in healthy, normal-weight middle-aged men and women. Metabolism. 2007 Dec;56(12):1729-34.

How much of your calorie budget goes to non-essentials? Discretionary calories explained

Over the last couple of weeks, the students in my discussion groups at UMass have heard (or slept through) my lecture on the food pyramid. I think that my readers might benefit from a little explanation as well. The food pyramid is pretty confusing, and there is a lot of information I could bore you with. But for now, I'm going to focus on what I think is the most important and least understood aspects of the pyramid: discretionary calories.

If you haven't seen the food pyramid in a few years, you probably haven't even heard this term. It is a new category, a substitute for the "fats, oils, and sweets" group depicted at the very top of the old food pyramid. Oils have now been recognized for their beneficial nutrients (e.g. essential fatty acids) and given a group of their own. The other fats and added sugars now comprise the "discretionary calories" (DC) group.

In a nutshell, DC are the calories left over after your nutrient needs are met. They are not unlike the money you have left after paying your bills; money you have for discretionary spending. These are the calories you can "spend" on whatever you like. The MyPyramid Plan site will tell you exactly how many of these calories you have to use each day, based on your age, BMI, gender, and activity level. For example, a 120 lb. lightly active 5'4" 25 year old female has a daily allowance of 195 discretionary calories.

One could use this allowance on approximately 6 oreo cookies. This may sound like a generous amount of junk food to be able to eat daily. But, what many people don't realize is that these nutrition-less calories are not only found in the obvious places-- cakes, cookies, fried foods, and the like-- but also lurking in less conspicuous staples of the American diet. For example, a cup of 2% milk has 41 DC, a single slice of cheese 83 DC, and a small hamburger patty has 74. Even seemingly harmless foods like low-fat yogurt (97 DC), granola bars (59 DC), and fruit sorbet (82 DC) can quickly whittle away your discretionary calorie allotment.

The important thing to remember about these calories is that they provide no valuable nutrients. They are truly "empty calories." All they do is give you more energy which, if not needed, will be stored as excess fat. The flip side of this is that foods high in DC tend to displace more nutritious foods. So, not only are you getting more calories than you need, but you may also not be getting enough nutrients because you are foregoing healthful things like fruits and vegetables in favor of the junky stuff.

If you want to know how much of your daily calorie budget you're spending on foods that don't do anything good for you, go to the MyPyramid site to find out your DC limit, and then check out MyFood-a-pedia.gov. It has a searchable database of foods with complete information about the food groups they belong to and their exact number of discretionary calories (called "Extras").

While I am at it, a final word on the food pyramid: I don't think it is anywhere near the best nutritional guidance we can come up with. For an alternative view, you may want to consult Walter Willett's Food Pyramid. This one is actually based on science, not input from agricultural lobbyists.