Metaslim Nutrition

On the BBC News website today there was an article suggesting that drinking a bottle of water before every meal can aid in weight loss. As usual the BBC declined to link to the actual study in question, so I had to do a bit of searching around, with no luck. Eventually I just emailed one of the authors who kindly pointed me to the study, published in a journal called 'Obesity' way back in February[1].

So, did the study actually show what the article claimed?

The researchers randomised 48 middle-aged to elderly men and women into two groups. Both groups were instructed to go on a calorie controlled diet, but one group was also instructed to drink a 500ml bottle of water before every meal. The trial lasted 12 weeks. Aside from two meals, one given at the start of the trial, and one at the end, the participants eating was unsupervised, although they were asked to complete 4 day food and activity reports. At the end of the trial, both groups had lost weight, but the group drinking the water had lost more, about 2kg on average, and 44% more than the control group.

I have a couple of issues with the article, the first of which is a key caveat of the study that the BBC decided was either unimportant or too complicated for their readers.

The problem here is that the study doesn't actually prove that it was the water that caused the additional weight loss. This might seem obvious at first but trials of this nature are always subject to a problem known as the intervention effect. This is the fact that simply being told to do something by the men and women in the white coats can have a powerful effect on our behaviour. It's why drug trials are always placebo controlled - without a placebo you cannot know what caused the effect you are seeing.

Look at it from the participant's point of view - before every meal they would drink a large bottle of water, which is a powerful mental reminder that they were participating in a dietary trial. This might encourage the participant to eat a bit less, either consciously or sub-consciously, and that could be the key difference between the two groups, not the water itself.

Now, I'm not criticising the authors here because they quite properly raised this issue themselves in the study: "It is possible that daily self-monitoring of water intake contributed to a greater weight loss in our water group participants, as others have demonstrated benefits of daily self-monitoring behaviors associated with weight management (i.e., daily self-weighing). Further research is warranted to determine the relative contributions of each of these possible physiological and behavioral mechanisms related to water consumption promoting weight loss."

In other words it's impossible from this study to know whether it was drinking water or the intervention effect that caused the additional weight loss.

You might now be saying, who cares? They lost more weight - surely the exact mechanism isn't important? To a dieter, maybe not, but the role of science is to accurately measure these kind of effects. As the authors said, further research is warranted.

For my other issue I want to go back to the article, because apparently one of the authors (erroneously cited as the lead author) claimed that "the reason water may be so effective is because it fills up the stomach with a liquid that has no calories." This smells like a classic case of a journalist goading a researcher into making speculative statements far beyond what has been tested. I think this kind of journalism is unfair on both the researcher and the reader. It distorts the accuracy of the article and presents hypothesis alongside fact without making a clear distinction between the two.

The idea that consuming empty calories can cause long-term weight loss is just a hypothesis - one that I disagree with.

Believing that we can control our weight by tricking ourselves into eating less at any one sitting is a very old idea. It's why some nutritionists recommend eating lots of soup or food with a high fibre content. While it's certainly true that we can reduce the calories consumed at a single meal in this way, thinking that this can lead to long-term weight loss is both un-tested and biologically implausible.

It's hard to test this in humans because of the intervention effect described above, but it was demonstrated conclusively at least in rats as far back as the 40s, in a series of experiments at the University of Rochester[2]. When the meals of the rats were diluted with water or clay, they either ate more of it or had smaller intervals between each meal. When food was injected directly into their stomach while they were asleep, they ate less when they woke. The driving force of their eating behaviour was the amount of calories their bodies required.

This should be blindingly obvious when you stop and think about it. A fundamental requirement of any living organism is to maintain a constant supply of fuel. We get hungry because we need energy. It's that simple. Yes, there are other psychological factors at work but they're not the driving force behind hunger. It's why we build up an appetite after exercising, or eat more when it's cold. It's why our metabolic rate slows on a low-calorie diet, and why most of us will regain any lost weight once we stop.

The body is constantly working to keep it's energy supply stable, and portion-size is only a tiny part of this complex, self-regulating system. If we skip a meal then we will eat more later in the day - so surely diluting the calories instead will have exactly the same effect.

1. Dennis, E. Water Consumption Increases Weight Loss During a Hypocaloric Diet Intervention in Middle-aged and Older Adults. Obesity, 2010;18:300-307
2. Adolf, E. Urges to eat and drink in rats. Am J Phys, 1947;151:110-125

Last week I attended a fascinating lecture by Dr. Tracey Green, hosted by Innovative Metabolic Solutions. The topic was the metabolic and hormonal consequences of the menopause and the appropriate diet and exercise programme to prevent obesity and muscle loss and reduce the risk factors of heart disease.

The scale of age related muscle loss (sarcopenia) may be a surprise. Without a change in physical activity 25% of peak muscle will waste away by the time we reach 60. By age 90, fully half of all muscle has degenerated. As the amount of muscle we carry significantly affects the amount of energy we use at rest (basal metabolism) then without a corresponding limitation in calorie intake weight gain is inevitable.

What this tells us is that low-intensity aerobic exercise designed to burn calories (jogging etc.) is likely inadequate to combat post-menopausal weight gain, despite it being by far the most popular form of exercise in the demographic. What Dr. Green recommended was a programme that includes a significant amount of weights work, in order to maintain muscle tissue. This also has the added bonus of improving bone density, another key concern for post-menopausal women. The idea of women in their 50s and 60s hefting weights may seem a little unusual, but it makes biological sense.

Many thanks to Dr. Green for the lecture.

Several years ago there was a attempt in America to get obesity classified as a disease, so that insurance companies would be responsible for treating it. Obesity is something that people cannot help, so they need medical help.

The main argument in opposition was a restatement of the common belief that obesity is a behavioural problem, i.e. people eat too much and are too lazy so being overweight is entirely their own fault.

I believe that both of these positions are wrong.

While I welcome all attempts to take obesity and overweight seriously, classifying it as a disease is misguided and unhelpful, as it makes people look at excess weight as the primary problem, most likely to be treated by drugs, surgery etc.

However, the alternative position of blaming obesity on the biblical sins of gluttony and sloth ignores the fact that our bodies are not supposed to be overweight. Considering all of the health and social pressures on us to avoid obesity, why doesn't anyone who suffers from excess weight just eat less, exercise more, and be thin? Unfortunately, decades of research and the experiences of millions of people tell us that it's not that simple.

I believe the correct way to look at obesity is to consider it as a symptom, not a disease in it's own right. As the science writer Gary Taubes memorably phrased it, obesity is a symptom of the 'disregulation of homeostasis', or to put it in more plain terms, it is what happens when our body stops being able to manage it's own food intake effectively. Obese people get hungry even with huge excesses of fat, so something else is going on.

Obesity is not a disease, it is a symptom. Only when we recognise this can we focus on treating the underlying conditions that produce obesity in the first place.