Weight loss mini-series
Part 2 – When counting calories doesn’t work
Many people struggle to maintain a healthy weight, despite following various diet and exercise plans. In this three part mini-series, we will take a look at the hormones involved in weight control, why cutting calories doesn’t work, and how cravings and addiction fit into the picture.
In this section we explain why reducing calorie intake doesn’t necessarily result in weight loss.
It is well known that consuming more calories than the body needs usually results in weight gain, however reducing calories doesn’t have the exact opposite effect. The body is more strongly programmed to avoid weight loss rather than to avoid obesity, so when calorie intake is reduced, the body responds with physiological changes to ensure any weight that has been lost is regained.
Short term calorie restriction
Social, cultural and psychological factors influence how much we eat, and for most of us portion size and food intake can fluctuate dramatically from one day to the next. The body is well-equipped to cope with these fluctuations, otherwise weight would go up and down on a daily basis in line with calorie consumption. It is true that creating a calorie deficit (i.e. using more calories than you are taking in) results in weight loss in the short term. But over time this is not an effective weight loss strategy because when we reduce our calorie intake, hormonal changes stimulate the appetite and reduce metabolic rate in an attempt to conserve energy and regain the lost weight.
So calorie controlled diets often appear to work at first, but dieters find that weight loss plateaus and even reverses when these compensatory measures kick in. In other words, losing weight is relatively straightforward. Maintaining weight loss, is not.
Longer term calorie restriction
So what happens with longer term calorie restriction? Weight loss following an extended period of dieting has been shown to cause long-term changes in the hormones that control appetite – discussed in part 1. These hormones can remain high for as much as a year after the diet has finished, which helps to explain why people who initially lose weight may go on to gain even more after the diet has stopped. A loss of body fat also causes a decrease in production of body heat and metabolic rate, which helps the body to more easily regaining the weight that had been lost.
Small levels of calorie restriction may work for those who are already close to an ideal weight, but for those who are overweight, larger restrictions will simply trigger these mechanisms for weight regain.
The bodyweight thermostat
The body is basically programmed to maintain a fairly consistent weight – i.e. not to gain or lose too much. You might think of it like a body weight thermostat – if weight goes up then hormones reduce hunger and appetite, and if weight goes down the body increases appetite and conserves energy. Conventional advice says that by cutting 500 kcal per day you will lose 1 pound per week. Initially your weight may go down, but then changes in the hormones and metabolism cause us to gain weight. So we cut even more calories and the body works even harder to try and make us gain weight. The only way to succeed in this battle is to turn the thermostat down, so for example if your body is currently working hard to keep you at 90kg, you need to re-set your body weight thermostat to 80kg. Once you reach the 80kg, the key in maintaining that weight loss is by balancing the hormones insulin and leptin, which are discussed in part 1.
Exercise to boost metabolism
We all know the importance of regular exercise to maintain a healthy weight, but many fitness apps focus on the number of calories burnt rather than the type of exercise being taken. High-intensity cardio results in an increase in the resting metabolic rate (i.e. the number of calories your body burns when at rest) for several hours. But building muscle also helps boost the resting metabolism without any extra effort on your part, since the body uses up three times more calories sustaining muscle than fat. Many dieters make the mistake of trying to do as much aerobic and cardio exercise as possible to burn calories, neglecting the importance of building muscle with strength training.
Different ‘types’ of calorie
Much of the current research suggests there is an advantage to creating diets based on types of food, rather than calorie content. Many dieters struggle with the concept of being asked to eat greater quantities of high calorie foods like nuts and seeds, as they have always believed that cutting calories and reducing fat intake is the answer. Without understanding the detailed science it can be hard to alter a fixed mindset, especially when dieters have seen apparent ‘results’ with cutting calories and do not make the link with subsequent weight gain a year or more later.
Calories from carbohydrate, fat or protein are metabolised in the body in different ways. Protein for example, uses far more calories in its breakdown that carbohydrate or fat. Protein and fat increase satiety (the feeling of ‘fullness’) and also reduce the speed at which glucose enters the bloodstream, thus controlling the appetite, balancing insulin and inhibiting fat storage. 100 calories of sugar will affect the body in a very different way to 100 calories of broccoli. This illustrates why there is little sense in aiming to consume a set number of calories per day, or thinking it is OK to swap the calories in an avocado for the equivalent number of calories from cake.
There is evidence that concentrating on the balance of macro-nutrients (protein, carbs and fats), energy density and glycaemic load of a diet, may help to prevent the compensation mechanisms from being activated. In other words, you could potentially eat more calories yet not gain any weight.
The low glycaemic diet and high protein/fat diets have become very popular in recent years, and when done correctly these can be very beneficial to a whole host of health conditions - not just weight control. Manufacturers have caught on to the demand for products that fit into these diet plans, and dozens of processed ‘convenience’ foods have been created to meet the macronutrient requirements of these diets. However, not fully understanding the underpinning science of a diet can lead to poor choices and nutrient imbalance, which could take months or years to manifest. There are also health considerations beyond weight control that need to be understood when starting a new diet programme - for example, while high protein may result in weight loss it also produces toxic waste products when it’s broken down in the body. At moderate levels the liver and kidneys filter out these toxins and remove them safely, but excessive protein puts strain on these organs over time.
For this reason it is advisable that anyone who is interested in such a diet is seeks professional advice from an experienced practitioner. If you are interested in learning more, or training to become a Nutrition professional, take a look at the courses offered by the School of Health.
Coming soon: Part 3 - Cravings and food addiction