Are calories in fat worse and harder to burn than calories from carbohydrates?

From: Larry DeLuca, EdM, CSCS

The difference isn't in how the calories are "burned" so much as in how excess calories are stored.

Excess carbohydrate calories must be converted to triglycerides before they can be stored as body fat. This process requires over 25% of the energy stored in the food. Thus, if you took in 100 Calories of pure carbohydrate in excess of your body's needs, you'd only store about 75 Calories worth of fat, since you used up some of the energy in the conversion process.

Fat, on the other hand, is fat to begin with. It only takes about 3% of the energy in it to put it up on the larder shelf, as it were. Thus, 100 Calories from fat in excess of your body's needs can end up as 97 Calories worth of saddlebag.

Remember that we take in nutrients of all sorts together, though - fats, carbs, and proteins. Thus, the most important factor over time is generally the total number of calories. However, if you keep the number of calories in your diet exactly the same and switch from a high-fat to a lower-fat diet you will generally notice a reduction in weight (assuming you were in caloric balance beforehand).

Also, what's the difference between fat and saturated fat? Is saturated fat just more calories concentrated? A prompt response is appreciated!

Fats come in several varieties, among them saturated, monounsaturated, and polyunsaturated. The saturated fats are named because they have all the hydrogen they can hold (i.e., they are saturated with hydrogen) and contain no double bonds in their chemical structure. The monounsaturated fats have one double bond (which could be broken by adding two hydrogen molecules), and the polyunsaturated fats have more than one double bond.

Unfortunately I'm not an expert on the subtleties of fat metabolism, but it has been well established that there is an increased risk of heart disease associated with high-fat diets, in particular those high in saturated fat. Diets high in monounsaturated fat, such as the Mediterranean diet, are thought to have a heart-protective effect, but there is still much research going on in this area.

For most healthy individuals, it's recommended that keeping total amounts of dietary fat below 30% (and having saturated fat make up no more than 10% of the total amount of fat consumed) can decrease the risk of heart disease. Individuals with different pre-existing conditions may have different nutritional requirements.

Simple sugars can pose a much greater risk to health than fats. It depends on several factors and it can become a very complicated issue - it would take a large book to completly cover this subject.

This tired old saw has been trotted out by quack doctors and complementary health practitioners for ages, but there's really not much evidence (from our understanding of either carbohydrate metabolism or the pathophysiology of cardiovascular disease or diabetes) to support the statement with respect to healthy individuals.

Individuals who are obese, diabetic, or have some form of impaired glucose tolerance may need to watch their ingestion of some foods, but for the general population the primary risks from sugary foods are tooth decay and obesity from an excess of calories.

For those who insist that "complex carbohydrates are better" it's important to differentiate among three areas of distinction when making any sort of argument:

Your thoughts above are, for the most part, correct. On the subject of which would take longer to 'burn', again, there is no simple answer. If you refer to 'stored' fat and carbs - carbs can be burnt off much quicker than stored fat - also, large amounts of fat can be stored by the body but only a small amount of 'sugar'.

Tehnically this is correct, in that the reactions involved in metabolizing carbohydrates can occur faster, but in reality it makes little practical difference, as the shifts in metabolic activity are so dynamic.

On the other hand unused sugar is converted into stored fat, very quickly - and the fact that the body stores very little sugar means that if it is not used quickly it will be converted into fat. Also, the body does not store fat unless insulin is released - which only happens when you eat sugar.

Insulin is always present in the bloodstream - just in varying amounts. There is no "on/off" switch to insulin, fat metabolism, fat storage, or any of these processes. They all occur simultaneously, with new fat being added to body fat stores while some body fat already stored is being broken down.

Fat on the other hand is calorie dense, but it digest much slower than sugars which gives you a time advantage.

What sort of time advantage? It is true that ingestion of fat simultaneously with carbohydrate can slow the absorption of carbohydrate into the bloodstream, and may be helpful for some people who have an exaggerated response to pure carbohydrate, but it's really not going to be the miraculous controlling factor in weight management, either.


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