The Diogenes study: Best diet for long-term weight loss
We talk to HFG editorial advisor, Professor Jennie Brand-Miller about the exciting results of a major study into weight loss that lasts and how a lower-GI, higher-protein diet can keep the kilos at bay.
The Diogenes ('Diet, obesity and genes') study is considered the world’s largest diet study. It was conducted across eight European countries and involved over 700 families with one overweight or obese parent and one healthy child (irrespective of weight).
The study involved adult participants undergoing an initial eight-week low-kJ diet to lose weight, with participants losing an average of 11kg. Those who completed the weight-loss phase, and their families, then followed one of five different dietary regimes for six months:
Group 1: Low protein/low GI
Group 2: Low protein/high GI
Group 3: High protein/low GI
Group 4: High protein/high GI
Group 5: Control diet
All the diets were low in fat (less than 30% of energy consumed). Each group had people drop out, but the higher-protein, lower-GI diet group had the lowest drop-out rate and also regained the least weight over the six months of the study.
The results of the diet study have been published in the New England Journal of Medicine. The diet study was a central pillar of the broader Diogenes project, a pan-European study into how obesity can be prevented and treated from a dietary perspective.
What was the aim of the Diogenes study?
The broader goal of the project was to undertake the most definitive study yet to pinpoint the best diet for preventing weight regain. More specifically, the aim was to determine whether a higher intake of protein or low glycemic index (GI) carbs (or a combination of the two) would help people who had lost a lot of weight maintain their new weight.
What were the key findings?
The principle finding was that a modest increase in protein and a modest reduction in the GI of carbohydrate foods led to a significant improvement in the maintenance of weight loss. In fact, the combination – compared to the other dietary regimes – had the lowest dropout rate. Those assigned to the lower protein and higher GI strategy re-gained the most weight.
Why is the higher protein and low-GI combination so effective? What differentiates it from other diets, like low-kJ or low-fat?
Low-kilojoule and low-fat diets ignore the fact that, kilojoule for kilojoule, some foods produce more feelings of satiety or fullness (a gram of protein is more satiating than a gram of carbohydrate or fat; and a gram of low-GI carbohydrate is more satiating than a gram of high-GI carbohydrate).
Conventional diets rely on counting kilojoules or grams of fat – an unnatural way to eat. In the Diogenes study, the subjects were told to ‘eat to appetite’ – or until they felt satisfied and full.
Does this diet help with weight loss as well as weight maintenance?
Our study at the University of Sydney found that both high-protein and low-GI carbohydrate diets [individually] were equally effective for weight loss, and both were significantly better than a conventional low-fat diet. Our combination diet (high-protein + low-GI) was good for weight loss but no better than either alone. Lots of research has been conducted, but further research is still needed.
What about when it comes to emotional eating? Does this diet help people who ‘comfort eat’?
The Diogenes study included people who had been overweight and obese for most of their lives. Emotional eating would have been a part of their lives. The high-protein/low-GI diet had the highest completion rate – an indirect indication that participants liked the diet and wanted to stick it out.
When I’m shopping, how can I tell which foods are low-GI and/or high-protein?
Most of us can spot a high-protein food without reading the label – lean meat, chicken, fish, eggs, nuts, etc. But these foods don’t contain any carbs, so it’s important to combine them with a carbohydrate food. You can expect most fruit, vegetables (except potatoes), dairy products and legumes to be a good source of low-GI carbohydrates.
Unfortunately, when it comes to breads, breakfast cereals, rices, grains etc, only a minority are low-GI. So look out for the certified low GI symbol on the label – an indication that this food is not only low-GI, but also healthy. Don’t make the mistake of assuming that all wholegrains are low-GI.
Do I need to eat low-GI and high protein foods at every meal for this approach to work, or can they be combined over the day?
It’s best to ensure there’s some of both on your plate – in a ratio of roughly 1g protein to 2g carbohydrate.
Do snacks need to be low-GI/high-protein too, or is it enough to follow the principle only at main meals?
Snacks can be one or the other (high-protein or low-GI), but try to balance them out over the course of a day. If morning tea is a piece of fruit, afternoon tea should be a handful of nuts.
Legumes, beans, peas, etc have the 1:2 Diogenes ratio of protein to carbs. Low-GI cereal with milk is perfect for breakfast. Yoghurt is always a good snack.
How does the diet work in the longer term? Is it sustainable?
In general, our appetite rules our weight. The hypothalamus in the brain is what drives our desire to eat and it eventually overrules even the most dedicated dieter. A sustainable diet is one that we can stick to in the long run, allows us to ‘eat to appetite’, includes our favourite foods and doesn’t require too much discipline and sacrifice. The high-protein + low-GI combination ticks all those boxes.
Is this approach for everyone?
The Diogenes high-protein/low-GI combination diet is certainly a safe and sustainable diet for pregnant women and young children. This diet can also be safely followed by most people with diabetes or cardiovascular disease – the exception being those who have kidney complications (seek a doctor’s advice if you are unsure).
The optimal ratio of protein to low-GI carbohydrate for long-term weight maintenance.