It’s not just about calories

NUTRITION can be a complicated business sometimes.

In assessing the healthiness of any food, there are many, many variables that come into play, including fat, sugar, fibre, vitamin and mineral content.

However, the parameter that almost always gets the most attention is the calorie content — the amount of energy the food contains per 100 grams. This is undoubtedly an important number — after all, the laws of thermodynamics dictate that if our energy intake from food exceeds our energy expenditure from physical activity, the inevitable consequence will be weight gain.

However, it’s now increasingly clear that the source from which these calories arise is also a critical factor in determining their health effects.

Energy sources

To understand this more fully, we need to first familiarise ourselves with some basics, most notably the calorie content of the different energy sources or “macronutrients”. Here, we see that while protein and carbohydrate both contain four calories per gram, alcohol has seven calories per gram, fat weighs in with nine calories per gram. These numbers represent the amount of energy released when a gram of each of these macronutrients is burned in a laboratory device called a bomb calorimeter.

In simple terms, such analysis allows us to see why “energy dense” fatty foods have received so much attention in recent years — the implication is that even modest amounts of these foods can contain lots of calories which ultimately predispose to weight gain. So that much is simple.

Health effects

What has also to be considered is the filling or “satiety” effects of these different energy sources, and, in this respect, there is clear evidence that starchy (high carbohydrate) foods fill us up better than fatty foods. The Germans discovered this phenomenon as far back as the 1930s, and referred to the tendency to eat greater amounts of less filling high-fat foods as “luxorkonsumption”.

However, of even greater significance to health are the different metabolic effects created by various sub-types of these energy sources; differences which are not captured by a simple discussion of their energy or calorie content.

For instance, you’ll notice that I have made no distinction between starch and sugar — both are carbohydrates, and both have exactly the same energy content at four calories per gram. Nor did I distinguish between saturated, monounsaturated, polyunsaturated, trans- and Omega-3 fats — all of these are fats, and all contain an identical nine calories per gram.

Beyond calories

In terms of overall health, however, we know that these different sub-categories of carbohydrate and fat elicit vastly divergent effects on bodyweight and health. For example, sucrose, the sugar we get in fizzy drinks, sweet foods and table sugar, is made up of a glucose and a fructose unit joined together.

The starchy carbohydrate we get from bread, rice, pasta, potatoes and breakfast cereals, however, is made up exclusively of glucose units joined together.

We now know that it’s the fructose content of sugary foods and drinks that’s responsible for many of their adverse health effects, including abdominal weight gain, inflammation, and elevations in blood fat. These nasty effects are even more pronounced when the fructose is taken in a liquid form (e.g. a sugary drink) that’s rapidly absorbed from the gut.

Similarly, research has shown that while saturated fats, from processed meats, cream and rich cheeses and especially trans-fats, from deep-fried foods, pastries, have unfavourable effects on bodyweight, inflammation and blood cholesterol levels, Omega-3 fats which we get from oily fish, like salmon, mackerel, herring, trout and sardines, generally have the opposite effect.

So, while limiting total calorie intake has obvious benefits for health, additional attention to the sugar (often labelled “sucrose” or “high fructose corn syrup”), saturated (“animal”) fat and trans- (“hydrogenated”) fat content of our food may achieve multiple additional health benefits that go far beyond calorie-counting and weight control.

* Dr Daniel McCartney, Lecturer in Human Nutrition & Dietetics at DIT.