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My understanding on diet and what foods I should be eating to maintain a low body fat percentage is very amateur. All this time I have just been looking at the calories in the nutritional facts label and if it's low I think it's fine to eat and if it's high I avoid it.

But I'm beginning to see there is a whole lot more to it than that. For example I have always eaten lots of white rice (it's my staple food) but now I see this type of carb is bad for weight loss. Not sure why though, something to do with being high in the gyclemeic index I hear.

My question is, what role does sugar and blood sugar levels play in weight and metabolism.

If I want to lose body fat I need to keep my metabolism high correct? So fat burns quicker rather than being stored.

How to speed up metabolism diet wise? Is it by avoiding sugars or always keeping blood sugar levels high?

Does it matter where the sugar is coming from, for example fruits vs raw sugar from a bag?

Any explanations are appreciated.

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I think this question is too broad to be answered in its current form. It's not clear what is being asked. –  Dave Liepmann Mar 20 '12 at 3:33
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Suggest some background reading first. Taubes' "Why we get fat and what to do about it" might be a good start. –  Greg Mar 21 '12 at 22:21
    
Off topic according to the FAQ since the scope change of the site excluding pure nutrition question. –  Baarn Sep 13 '12 at 14:43
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First of all, this question is really, really broad, which is why you haven't gotten any answers. Second, when you do find answers, they will likely be conflicting. Also, I am not a doctor, I'm just a person that has been dealing with weight/weight loss for a while, has a family history of Diabetes, and love to learn about as much as I can. Some may disagree, some more knowledgeable folks may correct me.

Here are some basics, though.

First, what is sugar?

The answer to this might seem obvious, but there are actually several different kinds of sugar, and they don't all affect the body the same way. The three you'll most commonly find are Sucrose, Fructose, and Glucose. Additionally, if you consume a lot of dairy products, you'll see a lot of Lactose ("milk sugar").

Sucrose is your typical "table (white) sugar." It's a disaccharide compound of Glucose and Fructose. For more information on all the details, Wikipedia is a good start.

Fructose is the sugar found in fruits and is a monosaccharide. Again, here's more info.

Glucose is the sugar that our bodies actually use. Like Fructose, it's a monosaccharide. Here's the wiki.

This is important because each one has an effect on our bodies. Sucrose gets broken down into its components.

From there (or if you just consume Fructose), the Fructose gets shipped to your liver for processing and the Glucose heads to your blood stream for the muscles to absorb and use for energy. The important part to note here is that fructose does not affect blood sugar levels. That doesn't necessarily mean that your body isn't doing anything with it (the liver is doing stuff with it), it just means that you won't get the same insulin response as you do with Glucose. Why is this important? Because Glucose and Insulin play a role in determining whether or not you're hungry.

So, in short: yes, it does matter where your sugar comes from, but probably not for the reasons you're thinking.

A note about High-Fructose Corn Syrup (HFCS) - In the United States, HFCS is a common compound used to sweeten processed foods. Nearly everything has it. It's controversial as to its effects and whether it's better or worse than other forms of sugar, but very often if will come up when looking for anything on Fructose or sugar in general. I won't go into that debate here, but I do want to point out the big difference between HFCS in the diet and getting Fructose from whole foods/fruit - the fiber content. Fruit contains a lot of fiber and very often, the sweeter the fruit, the more fiber it contains. When eating fruit, it's the fiber that helps you feel full. HFCS is devoid of that fiber, which is why "junk foods" made with it are often referred to as "empty calories" - they pack on the calories without making you feel full, because they're devoid of the nutrients that trigger the "full" response.

Where do carbs fit in?

Complex carbohydrates (or "carbs") are what you find in things like bread, pasta, and even vegetables. They are considered complex because they are compound molecules (a lot like Sucrose, but with more components). Ultimately, they get broken down into simple sugars, including Glucose.

This is where it starts getting hairy when it comes to carbs. Because it takes time to break down the carbs into their simple sugar components, you get a prolonged Insulin response as the body tries to keep the blood sugar levels in check.

Blood Sugar and Weight/Metabolism

Unfortunately, there isn't an easy answer to your question on this. If there was, we wouldn't have both low-carb diets like Atkins and moderate-high carb diets (nor would Atkins start advertising that they start introducing "good carbs" after the initial couple of weeks), and you likely wouldn't be asking this question to begin with.

Keep in mind, as well, that dysfunctional blood sugar and/or Insulin levels may lead to Insulin Resistance and even Diabetes. There is some speculation as to whether weight causes Insulin Resistance or Insulin Resistance causes weight gain (though, in my experience, Insulin Resistance is a precursor to Diabetes and can be reversed with proper diet and exercise), but it is something to keep in mind, especially if you're already at risk for Diabetes. (The New York Times ran a fascinating article a few years ago on carbs that is worth reading. In it, it explains the whole Insulin Resistance-weight gain-Diabetes spiral quite well.)

"Eat food, not too much, mostly plants"

Michael Pollan wrote that. I think it's a good rule of thumb.

When it comes to basic weight loss, it ultimately boils down to Calories in versus Calories out. If you want to lose weight, eat less than what you burn. ("...not too much...")

Quality, of course, matters. That's where the "eat food" part comes in. Eat real food. Toss out the Pringles, the Pepsi, and the Little Debbies, and stock up on the apples, strawberries, and carrots.

For this one, my interpretation of it is to make sure you're not just eating a meal of steak, or a hamburger with nothing on it. Include a salad with your meal, add tomatoes and lettuce to your sandwiches, etc.

The Macros - Protein, Fat, Carbs

For the most part, a diet with all three of the "macronutrients" or "macros" works best and is the most sustainable. Remember - dietary nutrients do not directly translate into the same-named physical attributes (for example, eggs have a lot of cholesterol, but the idea that they contribute to your body cholesterol levels (LDL/HDL) have been debunked). They each have their place in a healthy diet and none should be vilified.

What those percentages actually are will vary from person to person, though. Most recommendations I've seen say to start with a fairly even split - ~30% carbs, fat, and protein, give or take a couple of percentages. You can then tweak it from there based on what makes you feel the best and helps you achieve your goals. Some people thrive on a higher carb/protein and low fat diet, while others do better on a higher protein/fat and lower carb diet, and still others do best on an even split. It depends largely on your personal nutritional needs, which only you (and possibly your doctor) can determine.

What's best for weight loss? Eat less and move more. Get out and exercise, do strength training, and eat fewer calories than you burn throughout the day. For the most part, it really can be that simple.

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