Calories are important, but not the whole story…
by Kelly Bennett
We each need different amounts of calories to maintain a healthy weight and meet our nutritional needs, depending on our age, gender, weight, height, level of activity and individual metabolism (1).
The idea that a calorie is a calorie is a calorie, is very simplistic.
A calorie is a way of measuring a unit of energy. Technically, one calorie is the amount of heat it takes to raise one millilitre of water by one degree. Calories in food are generally measured in kcal, or the amount of heat it takes to raise one litre of water by one degree (2).
Fundamentally, we can gain weight if we eat more calories than we burn, because we store the extra energy as fat, or lose weight if we eat fewer calories than we use, because we burn fat stores for fuel (1).
The general guidelines are that an average man needs about 2500kcal daily, or an average woman about 2000kcal daily, in order to get the energy and nutrition they need (1).
But who is average?
A more personalised way of looking at calories, is to calculate your basal metabolic rate; BMR is the amount of calories or energy someone needs at rest, just for normal, basic, physiological functions. There is a mathematic formula called the Harris-Benedict formula, which uses gender, weight, height and age, to work out what someone’s BMR might be. This is the baseline level of calories you need each day. Then, you can adjust the number of calories you use daily, based on your activity levels (3).
This formula tells you roughly how many calories you personally need to maintain your current weight. If you want to reduce your weight, the advice is to reduce your calories by about 500 daily, which for an average woman would be about 1500kcal daily, or 2000kcal for men (or the inverse if you want to gain weight (1)).
However, for many people, reducing calories in order to maintain healthy weight, is not so simple:
Yo-yo dieting classically arrises if someone reduces calories too much, resulting in temporarily losing weight, but having a rebound reaction to the restriction, causing binging and weight gain.
Everyone’s metabolism is different and how we respond to calorie restriction is very individual. The basic advice of eating less calories and exercising more can be very difficult for people with metabolic issues.
One of the things which can affect someone’s ability to reduce calories, is how able they are to access their fat stores for energy; if someone has high insulin levels, it can be much more challenging for that individual to access their fat stores for energy than someone who has balanced or low levels.
Insulin is a hormone which helps us to regulate our blood sugar, by storing excess sugar from our blood stream as body fat. If we eat more sugar or carbohydrate than we need, we secrete excess insulin, potentially leading us to store excess fat. Some people naturally secrete higher levels of insulin in response to eating sugar or carbohydrates.
If blood sugar and insulin levels are high, we are likely to store fat, and it can be difficult to access our own fat stores. This can be one reason why people can struggle to lose weight on low calorie diets. If the diet is high sugar or high carbohydrate, but low calorie, it can be difficult to access reserves of calories in fat stores, causing hunger and cravings, resulting in eating a higher calorie intake (4). Therefore, it can be potentially useful if someone is struggling to reduce calories to look at moderating their blood sugar, carbohydrate and insulin levels, to help them achieve a healthy weight.
Some people who have a stronger insulin response to eating sugar or carbohydrates can find it much easier to reduce their weight on a lower carbohydrate nutrition plan. In some studies, a very low carbohydrate or ketogenic diet, where carbohydrates are under 50g daily, can reduce insulin levels and enable access to body fat stores better than reducing calories (5). It can be particularly useful if someone has type two diabetes or insulin resistance (6), however, it’s not for everyone.
Some people find a very low carbohydrate diet can trigger low energy, low mood, digestive issues, (7) or carbohydrate cravings and bingeing (8).
In my opinion, a much more moderate, sustainable and balanced approach, is to reduce carbohydrates to around 100 -150g daily. This roughly supplies the amount of carbohydrate physiologically needed, rather than less than needed, but not in excess, so fat storage is less likely, and insulin levels are balanced, enabling access to fat stores.
If you are struggling to maintain a healthy weight and find reducing calories too low can make you tired, irritable, anxious, moody and really hungry, I would suggest looking at how many carbohydrates you might be eating. Moderately reducing carbohydrates might enable you to access your body fat stores and make reducing calories achievable.
The main thing is to find a way of eating that is nutritious, sustainable and pleasurable, and works for you as a unique individual to maintain a healthy weight.
Kelly is a Registered Nutritional Therapy Practitioner who believes healthy nutrition is a gift we give to ourselves, and her approach is based in self-compassion rather than self-punishment.
The aim is to make healthy nutrition a self-nurturing and pleasurable experience, using an evidence based and personalised approach; Kelly will look at the various nutritional or lifestyle factors that might be contributing to how you are feeling, and work out a plan to try to improve things together.