What did the research involve?
The researchers needed to obtain several sets of data to fill their model. Data for UK deaths from coronary heart disease, stroke and cancer were obtained from the Office for National Statistics, the General Register Office for Scotland and the Northern Ireland Statistics and Research Agency. Information on the population's intake of foods and nutrients was obtained from two sources: the average intake of fatty acids, fibre, and fruit and vegetables for 2005–7 was derived from the Expenditure and Food Survey, while estimates of salt intake came from the National Diet and Nutrition Survey, 2006.
The modelling also incorporated several meta-analyses of individual studies looking at diet and disease risk factors. The researchers looked at reviews that had pooled data from randomised trials, cohort studies or case-control studies, giving priority to meta-analyses of randomised trials. These different studies were combined in the model to calculate the change in risk of disease for an individual who changes his or her diet. To estimate the change in health outcomes with a change in diet at a population level, the model used the difference between current average consumption levels and recommended levels of different foods in the UK.
What were the basic results?
In a general summary of the main findings, the researchers calculated that:
About 33,000 deaths a year would be avoided if UK dietary recommendations were met. There would be a reduction in deaths from coronary heart disease of 20,800 (95% credible interval 17,845 to 24,069), a reduction of 5,876 for deaths from stroke (3,856 to 7,364) and a reduction of 6,481 for deaths from cancer (4,487 to 8,353). About 12,500 of these avoided deaths would be in people aged 75 or under. About 18,000 of the avoided deaths would be men and 15,000 would be women. More than 15,000 of the avoided deaths (nearly half the total figure) would be due to increased consumption of fruit and vegetables. Reducing average salt intake to 6g a day would avoid 7,500 deaths annually. The greatest number of deaths avoided would be in Northern Ireland and Scotland, whose populations are furthest from achieving dietary recommendations.
How did the researchers interpret the results?
The researchers say their study suggests that increasing average consumption of fruits and vegetables to five portions a day is the target likely to offer most benefit in terms of deaths avoided. They also say that reducing recommended salt levels to 3g daily and saturated fat to 3% of total energy would achieve a similar reduction in mortality.
They conclude that their calculations based on the Dietron model are robust, pointing out that their estimate of deaths avoided is lower than a previous government survey which calculated that 70,000 deaths a year could be avoided if government dietary recommendations were met. The estimates could be used in calculating the allocation of resources for interventions aimed at reducing chronic disease.
This well-conducted modelling study used various data sources to link consumption of different dietary components with disease risk factors (for example blood pressure, cholesterol and obesity) and subsequent mortality from coronary heart disease, stroke and cancer. The study supports previous research showing that diet plays a crucial role in health and that a diet with plenty of fruit and vegetables, fibre and low fat and salt levels can reduce the risk of chronic disease, in particular coronary heart disease. However, its predictions are made at the population level. A model such as this cannot predict individual risk, which will depend on many factors, including family history, smoking and other lifestyle habits.
It is important to note that the figures are based on the estimates and assumptions made when using a mathematical model, and not on reality. As the authors themselves note, the modelling technique they used may have led to “some degree of double counting” and that, therefore, their estimate of reduced mortalities if dietary recommendations were met is likely to be an overestimate. Also, the accuracy of the model depends to some extent on the quality of the meta-analyses that were included, and the quality of the individual studies that were pooled within these reviews in order to establish associations between diet and particular disease risk factors.
Overall, this study supports current dietary recommendations and even though it cannot predict how diet influences risk for individuals, it does indicate that keeping to dietary recommendations reduces the risk of disease.
Dietary recommendations include eating five portions of fruit and vegetables a day (about 440g) and 18g of fibre (provided by wholegrain foods and some fruit and vegetables). It is recommended that salt intake is limited to a maximum of 6g a day and that a third of total energy is provided by fats, with saturated fat comprising 10%. The researchers point out that in 2007, according to the estimated average intakes in the sources they used, none of the UK countries met these recommendations.
Throughout the project, the families received expert guidance from dietitians and were asked to provide blood and urine samples.
Diogenes: The five diet types
The design comprised the following five diet types:
- A low-protein diet (13% of energy consumed) with a high glycemic index (GI)*
- A low-protein, low-GI diet
- A high-protein (25% of energy consumed), low-GI diet
- A high-protein, high-GI diet
- A control group which followed the current dietary recommendations without special instructions regarding glycemic index levels
A high-protein, low-GI diet works best
A total of 938 overweight adults with a mean body mass index (BMI) of 34 kg/sq m were initially placed on an 800-kcal-per-day diet for eight weeks before the actual diet intervention was initiated. A total of 773 adult participants completed this initial weight-loss phase and were then randomly assigned to one of five different diet types, where 548 participants completed the six-month diet intervention (completion rate of 71%).
Fewer participants in the high-protein, low-GI groups dropped out of the project than in the low-protein, high-GI group (26.4% and 25.6%, respectively, vs. 37.4%; P = 0.02 and P = 0.01 for the two comparisons, respectively). The initial weight loss on the 800-kcal diet was an average of 11.0 kg.
The average weight regain among all participants was 0.5 kg, but among the participants who completed the study, those in the low-protein/high-GI group showed the poorest results with a significant weight gain of 1.67 kg. The weight regain was 0.93 kg less for participants on a high-protein diet than for those on a low-protein diet and 0.95 kg less in the groups on a low-GI diet compared to those on a high-GI diet.
The children's study
The results of the children's study have been published in a separate article in Pediatrics. In the families, there were 827 children who only participated in the diet intervention. Thus, they were never required to go on a diet or count calories – they simply followed the same diet as their parents. Approx. 45% of the children in these families were overweight. The results of the children's study were remarkable: In the group of children who maintained a high-protein, low-GI diet the prevalence of overweight dropped spontaneously from approx. 46% to 39% – a decrease of approx. 15%.
Proteins and low-GI foods ad libitum – the way ahead
The Diogenes study shows that the current dietary recommendations are not optimal for preventing weight gain among overweight people. A diet consisting of a slightly higher protein content and low-GI foods ad libitum appears to be easier to observe and has been documented to ensure that overweight people who have lost weight maintain their weight loss. Furthermore, the diet results in a spontaneous drop in the prevalence of overweight among their children.
Citation: Thomas Meinert Larsen, Ph.D., Stine-Mathilde Dalskov, M.Sc., Marleen van Baak, Ph.D., Susan A. Jebb, Ph.D., Angeliki Papadaki, Ph.D., Andreas F.H. Pfeiffer, M.D., J. Alfredo Martinez, Ph.D., Teodora Handjieva-Darlenska, M.D., Ph.D., Marie Kunešová, M.D., Ph.D., Mats Pihlsgård, Ph.D., Steen Stender, M.D., Ph.D., Claus Holst, Ph.D., Wim H.M. Saris, M.D., Ph.D., and Arne Astrup, M.D., Dr.Med.Sc. for the Diet, Obesity, and Genes (Diogenes) Project, 'Diets with High or Low Protein Content and Glycemic Index for Weight-Loss Maintenance', N Engl J Med 2010; 363:2102-2113 November 25, 2010
This month the federal Department of Agriculture and Health and Human Services will release the 2010 dietary guidelines. These guidelines directly impact the eating habits of one in every four Americans whose meals are subsidized by federal programs. The precise timing of the release this month is unknown, according to John Webster, a spokesman for the USDA.
The major question here is whether or not the new guidelines will impact the obesity epidemic that is increasing ever so quickly in our country. Decisions about what to eat are generally made at the supermarket, not while reading federal guidelines. “What we need to do is put more effort into figuring out how to engage people who don’t use nutrition as a major deciding point when buying food,” says Alice H. Lichtenstein, a professor at the Friedman School of Nutrition Science and Policy at Tufts University. “We really need to learn more about consumer behavior.’’ Some experts wonder if more nutrition information helps or confuses shoppers.
It is arguable that the guidance needs to be much clearer, more like the wildly popular “Eat This, Not That!,’’ a magazine column, which was then reworked into a book and an iPhone app, that made its mark by telling readers which fast food was nutritionally better than others. Dr. David L. Katz, director of Yale University’s Prevention Research Center and an associate professor at the university’s School of Medicine, is an advocate for more specific guidance. For example, 45 to 65 percent of daily calories should come from foods that contain carbohydrates. But “lollipops and lentils are both carbs,’’ Katz says. And while the current federal recommendations do stress eating carbohydrates from whole grains, fruits, and vegetables, he adds, “We need to do a better job of specifically defining highly recommended foods.’’
While no one is talking about the final 2010 recommendations before their release, a June advisory report, open for public comment, gives some clues. Cohen of UMass Amherst expects the final guidelines to place even greater emphasis on physical activity and continue to recommend that people include more fruits, vegetables, nuts, seeds, foods with Omega-3 fatty acids, and a suggestion to eat three servings of low-calorie dairy products a day (some argue that calcium supplements should be used in place of the third serving).
Food-specific diets rely on the myth that some foods have special properties that can cause weight loss or gain. But no food can. These diets don't teach healthful eating habits; therefore, you won't stick with them. Sooner or later, you'll have a taste for something else – anything that is not among the foods you've been “allowed” on the diet.
The popular high-protein, low-carbohydrate diets are based on the idea that carbohydrates are bad,
that many people are “allergic” to them or are insulin-resistant, and therefore gain weight when they eat them. The truth is that people are eating more total calories and getting less physical activity, and that is the real reason they are gaining weight. These high-protein, low-carbohydrate diets tend to be low in calcium and fiber, as well as healthy phytochemicals (plant chemicals).
Some authors of these fad diets advise taking vitamin-mineral supplements to replace lost nutrients. However, supplements should “bridge the gap” in healthy eating and not be used as a replacement for nutrient-rich foods. Also, the authors of high-protein, low-carbohydrate diets advocate taking advantage of ketosis to accelerate weight loss. Ketosis is an abnormal body process that occurs during starvation due to lack of carbohydrate. Ketosis can cause fatigue, constipation, nausea, and vomiting. Potential long-term side effects of ketosis include heart disease, bone loss, and kidney damage.
Successful weight loss (losing weight and keeping it off for at least five years) is accomplished by making positive changes to both eating habits and physical activity patterns.
How can you spot a fad diet?
Weight-loss advice comes in literally hundreds of disguises. Most often the “new” and “revolutionary” diets are really old fad diets making an encore appearance. Examples of fad diets include those that:
- tout or ban a specific food or food group
- suggest that food can change body chemistry
- blame specific hormones for weight problems
Ten Red Flags That Signal Bad Nutrition Advice:
- Recommendations that promise a quick fix
- Dire warnings of dangers from a single product or regimen
- Claims that sound too good to be true
- Simplistic conclusions drawn from a complex study
- Recommendations based on a single study
- Dramatic statements that are refuted by reputable scientific organizations
- Lists of “good” and “bad” foods
- Recommendations made to help sell a product
- Recommendations based on studies published without peer review
- Recommendations from studies that ignore differences among individuals or groups
Source: American Dietetic Association