What is a calorie and why do they matter?

A calorie is the unit used to measure the energy supplied by various foods in our diets. If you look at any food label you will see the calories referred to as ‘kcal’. They are our ‘fuel’ and in the same way that a car needs fuel to move, we need fuel to function too. In case you missed the physics lesson on energy, here is the science: “energy can be converted to different forms, but it cannot be created or destroyed”. Therefore, if we think of food, the energy is usually in the form of carbohydrates, fats and protein. When we eat them, our body converts this ‘food energy’ into heat (thermal energy), movement (kinetic energy) and new tissues (chemical energy). So, basically, we need calories to stay alive!

Are all calories the same?

In terms of energy value, a calorie is a calorie. It is a set amount of energy – specifically, it is the amount that is needed to increase the temperature of 1g of water by 1°C. As mentioned above, the calories in food come mainly from the macronutrients: carbohydrates, proteins and fats. These nutrients are not equal in terms of their calorie value (alcohol also provides calories):

When it comes to nutrition, the quality of the food supplying the calories is very important. This is known as ‘nutrient density’ – in other words, for every calorie the food gives you, how many nutrients does it also provide?

A nutrient-dense food is one that carries a host of important nutrients relative to calories e.g. cheese; whereas a high calorie food, which is low in nutrients, is not considered nutrient-dense e.g. toffee. Therefore, food choice counts! In addition to needing fuel for energy, we also need it to help us function at our best by providing important nutrients. We wouldn’t put the wrong fuel in our car, so equally we should take care in choosing what fuel we put in our bodies!

How many calories in a glass of milk?

Dairy milk is one of the most nutrient-dense foods naturally available. When it comes to milk and calories, the calorie content depends on whether it is whole milk, semi-skimmed milk or skimmed milk (these are also often referred to as full-fat, low-fat and fat-free milk). Per 100 g, these each contain 63 kcal, 46 kcal and 34 kcal. For a simple comparison, 100 g of bread contains 219 kcal, 100g of banana contains 95 kcal and 100 g grilled chicken contains 148 kcal approximately. However, we don’t usually consume 100 g of every food and it is the totality of nutrients in these foods that gives them their nutritional value, as part of a balanced diet.

A typical serving size for a glass of milk is 200 ml and it provides a wide range of important nutrients including protein, carbohydrate, fat, calcium, riboflavin, vitamin B5, vitamin B12, potassium, phosphorus and iodine. The good news is that whole milk, semi-skimmed and skimmed milk are all a source of these important nutrients. The difference in the calorie content of these milks is mainly related to their fat content. For example, whole milk is standardised to have at least 3.5 % fat; semi-skimmed milk is standardised to have 1.5 – 1.8 % fat; and skimmed milk is standardised to have no more than 0.5 % fat. Therefore, as fat is calorie-rich, removing some of the fat content reduces the energy value of the milk.

A glass of milk – great value for your calories!

It is well known that there is much more than protein and calories in milk. In Ireland, dairy foods contribute to only 9 % of our calorie intake but it contributes to 39 % of our calcium intake. Milk is recognised as one of the best sources of this important nutrient, which is needed for the growth and maintenance of normal bones and teeth. In fact, 99% of the body’s calcium is found in our bones and teeth! Calcium also contributes to normal blood clotting, energy metabolism, muscle and nerve function, and it plays a role in the function of digestive enzymes and cell division!

Check out the diagram below to learn more about the many functions of other important nutrients in found in dairy:

Nutrients working together: Research on the ‘milk matrix’ is exploring how the overall health effects of these nutrients may be more effective when they are consumed together, as part of the unique dairy food structures.

Are all ‘milks’ the same?

Although they are often perceived to be similar or ‘lower in calories’, it is important to be aware that non-dairy milk-alternatives are nutritionally very different to cow’s milk. These alternative drinks are generally composed of water and ingredients such as soya, rice, almond, oat, coconut, hazelnut or hemp. Whole milk is generally higher in calories (63 kcal/100 g) compared to non-dairy alternatives but semi-skimmed and skimmed milk have comparable levels (46 kcal and 34 kcal per 100 g). The energy content of alternatives tend to vary depending on the addition of ingredients such as oil or sugar but is usually between 24-50 kcal per 100 g. Almond and coconut drinks tend to have the least calories, especially the unsweetened versions, but remember they are much lower in protein and lack other nutrients found in cow’s milk. To find out more about why cow’s milk is a more nutritious choice, read our article in Real Talk.

Milk – where does it fit in?

If you have dairy in your diet, you can be sure it is making a valuable contribution to your overall nutrient intake. As part of a balanced diet, the Department of Health’s guidelines recommends 3 servings from the ‘milk, yogurt and cheese’ food group each day. Typical servings include 200 ml of milk, 125 g of yogurt or 25 g of hard cheese. There are lots of ways that these can be incorporated across the day e.g. a delicious berry smoothie, a frothy cappuccino or a sprinkle of grated cheddar on your favourite pasta dish. Check out more recipe ideas here.

The chart below shows the nutritional contribution that ‘3-a-day’ can make to your recommended nutrient intake – very impressive considering three servings of low-fat dairy account for less that 15% of a standard 2000 kcal diet (whole dairy is less than 20%)!

Is drinking milk good for weight loss?

Foods with a high calorie or fat content are often referred to as being ‘fattening’. However, individual foods should not be categorised as fattening without taking into consideration how much of the food is consumed and what the overall diet is composed of. Weight gain is directly linked to an overconsumption of daily calories over time.

If you are trying to lose weight or simply tracking your calorie intake, it is important to remember that diet quality becomes even more important when you are eating less. Therefore, it is helpful to choose foods that provide the most nutrients per calorie. Low fat dairy foods are a good example, with a 200 ml serving of skimmed milk providing just 70 kcal. This equates to 3.5 % of the calories in a standard 2000 kcal diet. Therefore, drinking milk or eating dairy foods as part of balanced weight-loss diet can make a valuable contribution to your nutrient intake.

For more on nutrition, dairy milk and weight loss, check out our articles on Body Composition and Losing Weight.