Last updated April 18, 2018 at 9:22 am
Scientists have found that low-carbohydrate and low-fat diets have about the same weight loss success rates. We ask the experts how to navigate conflicting diet data.
609 people between 18 and 50 years old, about equally represented by men and women, participated in the study. They had a portion of their genome sequenced, and their baseline insulin measured.
The study: low-carb or low-fat?
In the first eight weeks of the study, the participants drastically limited their carbohydrate or fat intake depending on which diet they were assigned. Then, they were encouraged to add these elements back in until they reached a balance that fit their dietary restrictions yet was realistic to maintain long-term.
After 12 months, the participants had lost an average of nearly six kilograms, although there were some extreme results as well, such as a 27-kilogram loss and a nine kilogram gain.
The researchers could not find any connection between genotype pattern or baseline insulin and weight loss results.
Cut out processed food
Senior author Professor Christopher Gardner emphasised that the diets were carefully designed to be healthy. “We made sure to tell everybody, regardless of which diet they were on, to go to the farmer’s market, and don’t buy processed convenience food crap,” he said.
“Also, we advised them to diet in a way that didn’t make them feel hungry or deprived – otherwise it’s hard to maintain the diet in the long run.
“We wanted them to choose a low-fat or low-carb diet plan that they could potentially follow forever, rather than a diet that they’d drop when the study ended.
“On both sides, we heard from people who had lost the most weight that we had helped them change their relationship to food, and that now they were more thoughtful about how they ate.”
Professor Gardner and his team are keen to move on from the idea of genetically influenced nutrition and look for other useful solutions to healthy weight loss and maintenance.
“This study closes the door on some questions – but it opens the door to others. We have gobs of data that we can use in secondary, exploratory studies.”
The experts’ guide to navigating conflicting diet information
For the average person, it can be tough to know how to make the best decisions when it comes to nutrition. Here, scientists and experts react to this study and give some practical advice.
You can’t blame your genes
Dr Hannah Wardill, NHMRC CJ Martin Biomedical Research Fellow, University of Adelaide and the South Australian Health and Medical Research Institute
“As the rates of obesity rise with the notches on our belts, the amount of diets available for overweight and obese people is growing. It feels like we are increasingly bombarded with the newest, easiest, fastest and most effective diets for weight loss, and choosing the right diet is a difficult task for many.
Unfortunately, it still remains unclear which diet is the best for weight loss, and who the true demons really are… carbs or fat! What we do know is that some diets work better for some individuals than others, yet the factors that drive these inconsistencies remain unclear.
So, what’s the bottom line? Well, this is a large study, with good retention and substantial weight loss, so it was well positioned to detect interactions between diet types, genetics and insulin sensitivity. Unfortunately however, it has not taken us any closer to personalising weight loss strategies. So for now, you can’t quite blame your genes for not fitting in to your favourite jeans.”
Find a way to reduce your calories, because prevention is better than a cure
Melanie McGrice, Advanced Accredited Practising Dietitian, St Vincent’s Hospital Melbourne and Director of Nutrition Plus Women’s Health clinics
“This is a fascinating study as it challenges current thinking that genetically-modified diets will be the way of future, as many of us once thought.
The key points that I take away are that firstly, the type of diet doesn’t matter as long as the clients kilojoule intake is reduced, and secondly, that prevention is more important than cure.
Although genetics may not be able to influence weight loss, there is a significant pool of evidence which suggests that epigenetics do play a significant role in the onset of obesity, so I believe it’s important for us to focus on prevention of obesity in the next generation.”
There’s no best diet, consistency is key
Steve Pratt, Nutrition and Physical Activity Manager, Cancer Council WA
“This study confirms that weight loss is complicated and there is unlikely to be a magic solution based on someone’s biology. Participants in this study lost an average of five kilograms but the range was large, with some participants gaining weight.
This study suggest that it’s energy (deficit) that leads to weight loss regardless of the person’s genetic make-up or insulin biology. It also shows that there is no best diet for weight loss, with similar results for the low carbohydrate diet and the low fat diet.
This means people can choose an eating pattern that suits their preference (not their biology). It is likely that the best results were obtained by the people that stuck closest to the diets they were given. It has been shown consistently that the important factors for weight loss are energy deficit and adherence.”
Take care of your microbiome
Dr Laura Weyrich, ARC Postdoctoral Research Associate, Genetics and Evolution, the University of Adelaide
“While this research is a critical step forward for personalized medicine, the study did not address the most critical factor in the success of personalized dieting – the microbiome.
The trillions of bacteria that live within the human body – the microbiome – play critical roles in food digestion, regulating our hormone production, and are tied to human genetics.
It is likely that microbiome differences drove the previous findings that were tested in this paper. Your personal army of bacteria will need to be assessed if a diet can be effectively personalized for weight loss.”
Prioritise a diverse diet
Emeritus Professor Mark Wahlqvist, Director, Asia Pacific Health and Nutrition Centre
“The foremost dietary principle for humans, after being breast fed, is to have a biodiverse diet and to be physically active. This means we need small amounts of biologically distinctive and nutritious food commodities, which must inevitably be dominantly plant in origin.
The misleading and pointless macronutrient business of ‘carbs’, ’fats’ and ‘proteins’ then falls into place. This is a message relevant to both public health and clinical nutrition practice. Which is to say that most genetic heterogeneity is accommodated by the principle of dietary diversity and physical activity.
More important is what supports this approach. And that is a question of socio-ecological integrity. We are, after all, socio-ecological creatures.”
Personal preference and cultural background first, dietitian’s advice later
Dr Alan Barclay, consultant dietitian and nutritionist, Research Associate, The University of Sydney
“This study adds to the body of evidence that indicates that when it comes to weight loss, it’s the amount of kilojoules – not the carbohydrate or fat ratio of the diet – that is the most important factor.
In other words, provided the diet is reduced in kilojoules, and is composed of high-quality foods and beverages, the fat or carbohydrate ratio is not that important – you will still lose weight.
We can enjoy a variety of healthy cuisines from Mediterranean style to vegetarian style and still lose weight. The decision about which kind of diet to follow should be based on an individual’s food preferences and cultural background, and advice should ideally be provided by a dietitian.”
Choose nutrient-dense, high quality food
Dr Rosemary Stanton, Nutritionist, Visiting Fellow, The University of New South Wales
“This is an excellent study, randomised, well controlled, and with a large number of participants, lasting one year and involving genotype testing and important biochemical measurements including insulin.
Its major finding appears to be related to several facts: All participants were asked to maximise vegetables and minimise added foods with sugars, refined flour products or trans fats. They were also advised to choose high quality foods that were nutrient-dense and minimally processed, and, where possible, prepared at home.
Under these circumstances and with professional help and support to choose quality foods, the study shows that the macronutrient content of the diet does not really matter.
Some previous studies that have damned carbohydrates have not taken note of the foods that supplied it. For example, lentils and lollies are both ‘carbs’ but one is a nutrient-dense high quality food while the other is junk. Simply calling them ‘carbs’ does not provide this vital distinction.”
Creating healthy habits depends on your environment
Professor Lennert Veerman, School of Medicine, Griffith University
“The fact that the diets led to similar weight loss confirms earlier research that suggested that it doesn’t much matter what diet you follow (low fat, low carb, etc.) – they all work. It all comes down to consuming fewer calories.
A good rule of thumb is to avoid energy-dense foods and (especially) drinks: we eat to fill our stomach, and if that’s with vegetables we tend to lose weight, whereas if it’s with chocolate or French fries, flushed down with a soda, we gain weight.
While most diets work, the real challenge is sticking with them. The evidence suggest that after a promising start of the diet, people regain the weight they lost. Instead of ‘going on a diet’, it would be better to find new, healthier habits.
But for that to work, most people will need an environment that encourages healthy eating, rather than one that is full of heavily advertised, convenient and affordable junk food.
That is why the Cancer Council, Heart Foundation, the Australian Medical Associations and countless other health organisations argue for measures like restrictions on advertising and higher taxes on sugary drinks: it makes it easier for people to do stick to a healthy diet, and avoid the gradual weight gain that creeps up on most Australians.”
Expert comments gathered by the Australian Science Media Centre (AusSMC).
This study was published in JAMA.