After ploughing our way through a small mountain of our favourite foods on Christmas Day, many of us feel a guilty, nagging desire to shed the unwanted weight we’ve piled on in 2011. The only decision left is how to lose those pesky, persistent pounds. Should we follow a commercial weight-loss programme, or would one of the many diet books recommending a higher-protein diet be a more sensible option?
Although many people can shed a few kilos in the short term by following a low-calorie diet, few manage to successfully maintain their new weight, according to a 2007 review of dietary weight loss counselling in the Annals of Internal Medicine. We are up against the physiological changes that accompany weight loss: an increase in hunger and a decrease in our body’s resting metabolic rate. The problem with almost all diets is they leave the dieter feeling hungry for the best part of the day. And the hungrier we get, the more obsessed we become with food and eating.
This point was dramatically illustrated by a starvation study involving 36 conscientious objectors during World War II in Minnesota, America. These 36 healthy young men volunteered to lose a quarter of their body weight to provide scientists with insight into how starving civilians in Europe were affected physiologically and psychologically during World War II, and also how best to provide postwar rehabilitation.
These human guinea pigs ate a standard healthy diet providing about 13,400kJ (3200 calories) of energy a day for three months, before moving to a six-month semi-starvation diet that provided just over half that. As the diet progressed, the men’s initial enthusiasm waned; they became increasingly irritable and impatient with one another, had less energy and were less able to concentrate on tasks such as their university studies. Food became an obsession for the men, with several of them starting to collect cookbooks and recipes during the study. One managed to accumulate nearly 100 cookbooks and recipes by the time the Minnesota Starvation Study was over.
The study provides some important insights into the dieter’s world. The changes in mood observed in the Minnesota men, along with their new obsession with food, recipes and cookbooks, will strike a chord with many people who have dieted on and off for years and have a drawer full of recipes ripped from magazines and shelves overflowing with cook books.
But deprivation diets and gnawing hunger aren’t the best way to maintain a healthy weight. Rather, research has shown a healthy diet that prevents us from being hungry is the best option.
Does this ideal diet actually exist?
Given that protein satisfies hunger for longer than fats and carbohydrates, it’s hardly surprising high-protein diets have attracted attention. The Atkins diet has become the poster-child for this type of regime, but it’s not alone: the Zone diet and even the Total Well-Being diet, from Australian national science agency CSIRO, also recommend an increase in protein intake for losing the kilos and maintaining a healthy weight.
But should we really be dining like a Tudor royal, with meat on the menu for breakfast, lunch and dinner?
The protein-leverage hypothesis of Massey University nutritional ecology professor David Raubenheimer and colleagues suggests a lean beef steak for lunch might not be a bad thing. Their theory is that humans have a dominant appetite for protein, and when our food supply has a low ratio of protein to fat and carbohydrate, we tend to overeat, and this consumption of excess energy promotes obesity.
Raubenheimer, speaking in December at the Joint Scientific Meeting of the Nutrition Society of Australia and Nutrition Society of New Zealand, said studies of other vertebrates, along with human experiments and population-level studies, suggest that when faced with nutritionally unbalanced diets, we prioritise our protein intake. In other words, we keep on eating until we’ve ingested enough protein.
Therefore, in a world where the cheapest, most palatable and most widely available foods are high in carbohydrates and fat, rather than protein, we can easily be effectively trapped on a suboptimal diet, Raubenheimer’s 2005 study, published in Obesity Reviews, suggests. In these circumstances we would be driven to eat more food, over-consuming carbohydrates and fats to maintain the amount of protein we need.
And as protein is only a small component of the total diet, a relatively small reduction in the amount of protein in our food supply leads to a substantial excess intake of carbohydrates and fats, according to the protein-leverage hypothesis. Raubenheimer’s calculations suggest if the amount of protein in our food supply drops by just 1.5% and our carbohydrate and fat intake rise accordingly by 1.5%, we are likely to over-consume carbohydrates and fats – eating about 14% more – to maintain our protein intake.
A recent clinical trial, published in the journal PLoS One, tested Raubenheimer and colleagues’ protein-leverage hypothesis. Twenty-two lean adults were recruited for three four-day sessions of “in-house dietary manipulation”. This involved eating as much food as they wanted from a randomly assigned menu of 28 different foods. The menus were designed to be similar in palatability and acceptability but to differ in the amount of energy they provided from protein, ranging from 10% to 25%. The participants’ nutrient and energy intake was then calculated based on how much food they had from each of the menus.
What they found added more weight to the protein-leverage hypothesis: lowering the protein in the diet from 15% to 10% resulted in the participants increasing their total energy intake by 12%. The researchers concluded that changing the dietary environment by reducing the amount of available protein, and increasing the amount of carbohydrates and fats in foods, encourages overeating and therefore increases the risk of gaining weight.
That many Western countries have seen an increase in obesity alongside a reduction in the amount of protein in their food supply should come as no surprise. As Raubenheimer and colleagues point out, “the countries where the percentage of protein has risen most are those with the lowest incidence of obesity”.
Interestingly, the socio-economic implications of the protein-leverage hypothesis also provide a degree of support. Protein-rich foods, such as lean meat, fish and dairy products, tend to cost more than foods high in carbohydrates or fats.
This is why people on lower incomes are considered more likely to consume a diet lower in protein and higher in inexpensive processed foods that are high in fats and carbohydrates. And given a theoretical biological drive to eat enough protein, they are likely to find themselves driven to overeat and therefore gaining weight. In New Zealand and many other Westernised countries, obesity is more prevalent among lower socio-economic groups.
What about GI and protein?
Finding out whether a higher protein diet helps maintain weight was an aim of the pan-European Diet, Obesity and Genes study (Diogenes). A randomised study across eight European countries, it put 938 overweight adults on a low-energy diet for eight weeks. Participants lost an average of 11kg. The adults were then assigned to one of five different diets with high and low proportions of protein, and foods high and low on the glycaemic index. (The glycaemic index is a measure of how quickly carbohydrates break down in the blood. Low on the index are foods that break down slowly, including most fruit and vegetables and whole grains.)
Those on the high-protein, low-glycaemic-index diet had one of the lowest dropout rates and were the only participants to maintain their weight loss. Those on the low-protein, high-GI diet gained the most weight and were more likely to quit the diet.
The use of a high-protein, low-GI diet also resulted in a 14% reduction in the numbers of children who were overweight or obese among a group of 800 involved in the study.
The researchers concluded that a small increase in protein accompanied by a change to lower GI carbohydrates was best for both. In practical terms this means adopting a diet containing rich sources of protein – for example, lean meat, fish, low-fat dairy products and/or vegetarian alternatives such as legumes and beans – and fewer refined starches such as white bread and white rice.
How much protein are we talking about? According to the Diogenes researchers, the optimum for weight maintenance would be to get about 20-25% of energy from lean protein sources, with 25-30% from fat and 45-55% from fibre-rich wholegrain carbohydrates.
But this differs from the Ministry of Health’s dietary recommendations for optimising health and lowering the risk of chronic disease, which suggest 15-25% of energy should come from protein sources. However, these figures reflect ministry concerns about the role of protein in cancer risk, especially from eating large quantities of red meat. The World Cancer Research Fund recommends eating less than 500g a week of red meat, with little if any of that being processed meat.
Though the difference between the protein ranges recommended by the Ministry of Health (15-25%) and the Diogenes study (20-25%) might seem insignificant, this may not be the case if the protein-leverage hypothesis is correct. This is because the ministry’s five-percentage-point lower recommendation could make a significant difference to overall energy intake by encouraging over-consumption of carbohydrates and fats and increasing the risk of weight gain and obesity.
And given the 2008/09 New Zealand Adult Nutrition Survey found we are averaging just 16.5% energy from protein, there is good reason to wonder whether we are eating enough protein and whether our lower protein intake is contributing to the country’s growing obesity problem.
Behavioural strategies are the key
What we eat isn’t the only problem when it comes to maintaining a healthy weight. How we eat is a major issue, too. Do we eat when sad, tired, emotional, angry or bored?
Is our pantry full of fatty foods we find hard to resist an hour before dinner? Do we have unrealistic goals about what weight we should be?
To successfully maintain a healthy weight throughout life, the key is to create strategies that help to promote positive lifestyle and eating behaviours and overcome any bad habits that are sabotaging that goal.
The New Zealand Dietetic Association recommends all weight-loss programmes incorporate behavioural support that involves: identifying problem behaviours and the circumstances in which they occur; creating specific, achievable goals that are revised as progress is made; monitoring target behaviours; and possibly also including cognitive strategies that help modify any thinking that is a barrier to positive change.
Weight-loss programmes that focus on behaviour change are generally more successful than those that don’t, according to a 2011 systematic review in the Annals of Internal Medicine. It found that people who followed behavioural-based approaches lost an average of 3kg more than those who didn’t.
A number of commercial weight-loss programmes include behavioural strategies to increase their effectiveness. Comparing the effectiveness of a programme of this type with primary care by a general practitioner team was the focus of a study published in the September 2011 Lancet.
A total of 772 overweight and obese adults from Australia, Germany and the UK were randomly assigned to receive either 12 months’ standard care from their GP, or 12 months’ free membership to Weight Watchers. The participants were then followed up for a further 12 months.
The participants assigned to a local general practice received weight-loss advice based on national clinical guidelines for their country, so there were some variations. The Weight Watchers programme promoted a low-calorie balanced diet with increased physical activity, and offered behavioural strategies such as monitoring through regular weighing, and group support.
Over the 12-month period the Weight Watchers participants lost on average 6.65kg, more than twice as much as the standard-care group’s average of 3.26kg. The commercial weight-loss group were also more likely to lose more than 5% of their initial weight and had greater reductions in waist circumference and fat mass, both of which reduce the risk of diabetes and cardiovascular disease. Nonetheless, a quarter of patients assigned to the standard-care group also managed to lose 5% of their body weight, a significant achievement.
A comparable US study, published in 2010 in the Journal of the American Medical Association, looked at whether the Jenny Craig programme promoted greater weight loss and better weight maintenance than the usual public health care regime of a one-hour session with a dietitian, who provides basic information on a healthy diet and monthly updates via telephone or email. At follow-up some 24 months later, the participants assigned to the commercial programme had maintained a weight loss of around 7kg, more than three times that of the usual care participants who managed just 2kg.
A 2007 study, published in the journal Obesity, also found the Jenny Craig programme facilitated about a 7kg average weight loss among a group of overweight and obese women over a 12-month period.
The researchers say the benefits resulting from the commercial weight-loss programmes could be the result of the more intensive behavioural treatments, such as self-monitoring, goal setting, nutritional advice, exercise education, problem solving, stimulus control, and relapse prevention. The peer support element of some commercial weight-loss programmes may also be beneficial for some people.
The good news, then, is that with only relatively small changes to the types of food we eat and a concerted effort to improve our food behaviours, we stand a good chance of maintaining a healthy weight throughout life.