Dieting for Weight Loss
Most of us have gone on a diet to lose weight at some point in our lives, but was it successful? Did you lose weight—and if you did, did that weight stay off? Unless you are very unusual, all the evidence suggests that the answer to at least one of those questions is likely to be no. Dieting for weight loss is one of the big non-success stories of our time.
There are hundreds, if not thousands, of diet systems available, such as the Atkins diet, the 5/2 diet or Slimming World. They provide lists of what you can have for breakfast, lunch and evening meals, often with specialist cookbooks and ingredients. We buy the lists and the systems—and often we even reach that all important target weight. However, we then relax, and regain all the lost weight again, usually faster than it was lost.
It’s not completely unreasonable. After all, you can’t live on pineapples and celery salad for ever, can you? It’s not healthy.
This page explores why this happens, and busts some of the key myths exploited by the diet industry. More importantly, perhaps, it suggests some ideas for eating more healthily, encouraging your gut microbiome, and perhaps, just perhaps, losing weight naturally.
Myths about Weight Loss
There are many common myths about weight loss. Many of these are actively encouraged by the diet industry, because they keep us coming back for more.
However, most of them are wrong, and some of them are downright harmful.
Myth 1. If you use more calories than you take in, you will lose weight
The energy we get from food is measured in calories (Cal or kcal). All food provides us with energy, so all food has a calorific value.
The amount of energy we use is also measured in calories. Our bodies use energy to survive, to breathe, to walk or run, to talk and think. We use calories all the time, regardless of what we're doing.
The ‘golden rule’ of weight loss was therefore thought to be that if you used more calories than you took in via your food, you would lose weight.
This is (kind of) true, in that if you eat too much, you will probably gain weight. However, there are several problems with this theory of weight loss, including:
The calorific value of food is not the whole story
Calories in food are measured by burning the food in question within a piece of equipment called a ‘bomb calorimeter’, and measuring the amount of energy given off as heat. The problem is that we do not burn food in the same way, and the energy is not simply released as heat. The calorie count is therefore of very limited value in telling us how our bodies might deal with a particular food.
For example, a lot of the fat found in walnuts is not accessible to the body. This means that a lot of the calories contained therefore pass straight through. Second, our page What are Carbohydrates? explains that the structure of food matters in terms of how we metabolise the nutrients contained within it. More natural (that is, less processed) foods generally contain a stronger ‘food matrix’. It is therefore harder to access the nutrients. It takes longer to release them, and our bodies deal with them differently. A fruit smoothie, for example, has a very different effect on our body from a whole piece of fruit, but has the same calorie count. There are far more calories accessible to us in the smoothie, and they are in the form of glucose and fructose, with no fibre to slow down the absorption.
We are far more likely to get a damaging blood glucose ‘spike’ and then a subsequent low from a smoothie than a piece of fruit, and also to take in more calories. Glucose spikes are linked to food cravings and feelings of hunger—and therefore we consume more food. A smoothie therefore contributes a lot more calories than the same fruits in their natural form.
There is more about this in our page on Complex Carbohydrates, Sugar and Diet.
There is huge individual variation in the calories that we need just to stay alive
Government guidelines generally recommend that men need around 2500 calories per day, and women around 2000. However, researchers have found that the base metabolic rate of different individuals—the amount of energy we need just to run our bodies each day—can vary from about 1400 to 1900 calories. How can a single value work as a guide for everyone?
Restricting your food intake reduces your metabolic rate
When you restrict your food intake by reducing your calorie intake, you force your body into ‘survival mode’. Your metabolic rate reduces, and you therefore use fewer calories just to stay alive. This means that you need to eat even less—and that creates a vicious cycle. In fact, studies have shown that it can take years before your metabolic rate recovers from crash dieting. Reducing your calorie intake therefore has the opposite of the desired effect.
Myth 2. You can lose weight by cutting out whole groups of foods
Over many years, various diets have suggested cutting out whole food groups entirely.
There are many diets that focus on reducing fat intake, although the fat is often replaced by sugar. Others, like the Atkins diet, restrict carbohydrate intake. There are many people that swear by weight loss from both methods.
The problem is just that: both methods work, but for different people (see box).
When averages mask the story
One study compared two groups of people, one given a high-fat diet, and one a high-carbohydrate diet.
On average, neither diet had much effect. There was no significant average weight loss in either group and no significant difference between the groups.
However, when the researchers looked beyond the averages, they found some really interesting results. In both groups, some people had put on weight, and others had lost significant amounts.
In other words, for some people, a high-fat diet was key to losing weight. In others, that same diet caused them to gain weight.
We now know that our gut bacteria, or microbiome, plays a huge part in how we digest different foods, and deal with different nutrients within them. Some people are better able to manage fats, and others have a higher propensity for dealing with carbohydrates.
There is absolutely no ‘one size fits all’ in nutrition, which is why there is no single diet that works for everyone.
There is another problem with excluding whole food groups: the effect on our metabolism.
For example, ketogenic diets work by excluding carbohydrates. However, in practice, that means you have to eat a lot of fat, to force your metabolic system to move to ketosis, rather than the more usual glucose-based metabolic pathways. This means you can’t eat many vegetables, because they contain quite a lot of carbohydrates. That will limit your fibre intake, which is unhealthy for your digestive system and for your body more generally (there is more about this in our page What is Fibre?). Your meat and protein intake will also be restricted because protein can be turned into carbohydrates, which prevents ketosis.
The real issue here is that this is not sustainable in the long term. A study in the US compared two diets, ketogenic and Mediterranean (whole grains, lots of fresh vegetables, some meat and dairy). Each group followed one diet for 12 weeks, then the other for the next 12 weeks, and finally were left to their own devices for 12 weeks.
After 36 weeks, despite good intentions, nobody was still on a ketogenic diet, in the sense that they were in ketosis. They simply didn’t have enough food options to choose from.
Instead, they were effectively back on a diet containing carbohydrates. However, those carbohydrates were generally at much lower levels than before, and with far fewer refined sugars involved.
In other words, cutting out whole food groups is not possible or healthy in the long term.
Myth 3. Exercising will help you lose weight
Back to the idea of calorie counting: the concept was that there were two ways to balance the calorie equation. The first was to eat less, and the second was to move more.
It will probably be no surprise to learn that increasing your exercise is no more successful in terms of weight loss than reducing your food intake. The issue here is that the energy required to exercise is a very small amount of your overall energy requirement. You actually need far more energy just to stay alive than to go for an hour’s run.
We also tend to over-estimate the energy consumed during exercise, and underestimate the calories in food. Even an hour-long run will not be enough to justify that Mars Bar afterwards. You may also feel more hungry after exercising anyway.
There are two other factors that may also be creating a problem linked to exercise for weight loss.
We have been convinced by food companies that ‘energy drinks’ are good for us, especially after exercise. In reality, these are just sugary soft drinks that are likely to give us a sugar spike.
Muscle weighs more than fat. This means that you could be exercising, and becoming healthier—and a healthier shape—but not losing any weight. This is where it becomes important to use other methods of measuring the effects of your diet and exercise, such as how your clothes fit, or how you look and feel, rather than simply weight.
Exercise matters for more than weight loss!
Regardless of its effect on weight loss, exercise is really good for you. It helps to improve your general fitness and wellness, improves your heart health, helps you to sleep better, and improves the efficiency of your sugar metabolism, helping to reduce the risk of diabetes.
Even if it isn’t helping you to lose weight, exercising is a really good idea!
See our pages The Importance of Exercise and How to Exercise Safely and Effectively for more information.
Myth 4. If you fast intermittently, you can eat exactly what you like the rest of the time
One of the most popular dieting trends in recent years has been something called ‘intermittent fasting’, which restricts not what you eat, but when.Examples include the ‘5/2’ diet, which requires you to fast for two days, but you can then eat whatever you want for the other five days a week. Other versions allow you to eat whatever you want during, say, an eight-hour period of the day, but then absolutely nothing during the remaining 16 hours of every day.
First, there is no question that intermittent fasting can be a really good weight loss tool—and also that it has other benefits for health.
It seems to work because it simply changes what you do. The precise window in which you eat is up to you, but the key is to keep it fairly tight: eight to ten hours maximum. This seems to be fairly easy to sustain in the long term because your body gets into a routine.
Like many other diets, this works by restricting your eating. You can’t eat as much in an eight-hour window as you can in 12 or 16 hours. Similarly, if you really eat more or less nothing for two days each week, your food intake is inevitably going to be lower than if you ate ‘normally’ all the time.
However, you still have to be sensible in the windows in which you are allowed to eat. You still have to eat healthily—lots of fresh fruit and vegetables, and limited processed food, for example. Consuming a whole boxful of muffins in one sitting is not going to support long-term weight loss.
So no, you can’t eat exactly what you like the rest of the time—but with care, this is a pretty powerful weight loss tool, and one that works for a lot of people.
The Real Answer to Weight Loss?
What connects all the successful weight loss tools is that they are not a brief change in eating habits.
Instead, it seems to be helpful to think about developing new long-term eating habits: a lifestyle change rather than a diet. When people talk about 'going on a diet' they tend to aim for a target weight and then, when they reach their goal, revert to their previous eating habits and often regain some weight.
If you change your eating habits permanently—whether what you consume, or when, or how—you will find it easier to manage your weight in the future.
The second issue with losing weight is that we are all individuals. There is no single approach that will work for everyone.
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Research emerging from the ZOE study suggests that a highly personalised approach is necessary to eating, and that this includes for weight loss.
In other words, it is possible to lose weight and maintain that weight loss. However, you need to do it in a way that is tailored to you. You need to eat the foods that suit your body, metabolism and most importantly, your gut microbiome. Intermittent fasting may be helpful, but only if that works for you.
This is not like a crash diet, where you spend a few weeks losing weight and then return to ‘normal’. This is a long-term change. This may sound tricky, but all the evidence suggests that it is likely to be the only weight loss method that really works in the long term.