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Low Carbohydrate versus Low Fat

Picture of Orla Walsh, RD
Orla Walsh, RD
Orla Walsh is a Registered Dietitian and Physiologist. Orla is the founder of Orla Walsh Nutrition, she is the former performance nutritionist to the Irish Olympic team and is regular contributor for the Irish Independent newspaper, RTE and Newstalk FM.

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Diet trends have changed tack across the years. For a time people were following a low fat diet, which moved onto low carbohydrate high protein, then high fat diet, low carbohydrate and low protein (aka keto)… The list goes on and on!

The key to success is finding a dietary concept that suits you, that you can stick and that gives your body all the nutrition it requires. In other words, what works for one person may not work for another. In fact, if you hear someone peddling one diet in favour of another, they’re often wrong. There is no one-size-fits-all.

Science, Not Fads

Due to the confusing and conflicting information online, people are more unsure than ever. Evidence-based nutrition, which a Dietitian always encourages, is a means of looking at the available studies to understand whether certain diets work, just as medical professionals do with medications. The great news is that a really well conducted study has finally shed some light on whether we should all be following a low fat diet or whether a low carbohydrate diet is the best approach for us. This is great news, as many people jump on one or other of these dietary band wagons.

Which diet leads to best results?

Firstly, it’s important to note that this study followed on from a previously conducted study in 2007 comparing four different types of diet; Atkins, Zone, Ornish and a health professionals diet.

After a year of following one of the dietary plans, there was only a couple pounds difference between each group. This showed that all diets had a similar result. What was much more interesting was that when the researchers plotted every person out on a graph, they were able to see that there was significant individual variability between diets.  After much analysis they discovered what looked like a possible genetic predisposition that suggested one of 3 genes might be able to predict how well people would do on a particular diet. They also noted that there was possibly a link between insulin resistance and how well a person did on each diet.

Personalised Nutrition

The DIETFITS study followed on from this research with the aim of gaining more insight into this area. It is often reported as a study that aimed to investigate which kind of diet works best, low carbohydrate or low fat. However, the researchers themselves focused on investigating whether certain genes and insulin resistance would help dictate which diet works best for a particular person. In other words, could you prescribe a diet based upon certain genes or metabolic markers. 

Over 600 people joined the trial and were randomly assigned to follow either a healthy low fat or a healthy low carbohydrate diet for 12 months.

The type of trial is called a randomised clinical trial. The researchers compared two groups. One group followed a healthy low carbohydrate diet and the other group followed a healthy low fat diet. Each group had similar experiences, bar the diet they were following. Therefore, any differences in results can be put down to the diet they were following rather than potentially interfering factors.

A Look At The Study

Overall this was a well conducted, well funded extensive study. One of the best bits of this trial is that they focused on food quality. They aimed to increase the quality of the food that all of the participants ate. As you may know it’s possible to follow an unhealthy low fat diet and an unhealthy low carbohydrate diet. Therefore, the researchers reduced the probability that one particular diet was more successful that the other due to the quality of the nutrients and food eaten.

Like most studies, there were people dropping out. It’s worth noting that there were roughly equal numbers dropping out from each group. Therefore, it wasn’t a case that one diet was harder to follow when compared to the other. Both diets were purposefully made easier to follow to try and prevent drop off rates. This is important for many reasons, to avoid waste of funds as this study was expensive, internal validity for statistical analysis, to confirm that both studies were as easy to follow and to create meaningful, practical, applicable results.

What Was The Diet Program

Across the year, while following one of the diets, both groups had 22 sessions led by Registered Dietitians. Both groups were encouraged to maximise vegetable intake, minimise added sugars and refined carbohydrates. Therefore, both groups aimed to minimise processed foods and rely more on homemade meals made from wholefoods. They were also encouraged to exercise regularly and avoid mindless eating such as eating in front of televisions, computers and looking at their phone. Additionally, the Dietitians provided tips and support to help keep up their healthy habits. 

The focus on the dietary plans was limbo, titrate and quality. 

Limbo Diet

Initially participants kept up their normal habits before they were instructed to follow the limbo segment of the study. During limbo the participants had to bring their dietary intakes down to either 20g of carbohydrates per day or 20g of fat per day for 8 weeks. This was more of a psychological anchor rather than an evidenced based target. They were given guidance on how best to achieve this.

Titrate Diet

Then, after 8 weeks they were asked if they could stay at this level of restriction for another week. Some said no, others said yes. Therefore, the participants decided which week they then slowly increased the amount of carbohydrate or fat they ate until they reached the lowest amount they believed they could maintain over the long-term. This was referred to as the titrate stage as they increased their intake by about 5 to 15 grams per day for a week. They were never asked to count calories. They were encouraged to simply focus on their own hunger levels. At these new levels, if they still felt hungry they were encouraged to make another increase.  The end number of grams of fat or grams of carbohydrate was different for everyone. The limbo stage felt like a diet, but the titrate stage was meant to be more an eating pattern rather than a diet.

Weight Loss Results

After all was said and done, there was no difference between a healthy low fat and a healthy low carbohydrate diet. Both studies resulted in an average weight loss of 12 pounds (just under 1 stone). However the weight range ranged from 60lb loss to 20lb gain. This is an 80lb range of response from the same instruction! In both groups some people lost no weight, and others gained weight. 

Interestingly, neither the genes they chose to look at nor insulin appeared to have any effect on the response to each of the diets. This doesn’t mean that genetics don’t matter, it just means that these 3 particular genes which they thought may be meaningful appeared not to be. More studies need to be conducted to help personalise a nutrition approach to genetics.

Take Away

A big take home from this study, other than it didn’t matter what diet plan you followed as long as you could sustain it, was that education and support alongside realistic goals make for a great weight loss intervention.

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