At best out dated, and at worst deliberately misleading, there is plenty of misinformation within the fitness industry. To stand apart from this, many trainers and ‘internet gurus’ are now firmly in the camp of ‘evidence based’ or ‘scientifically based’ information, making their claims solely on the basis of peer-reviewed studies, RCT’s and meta-analysis, published in academic journals.
How then, even within the ‘scientific community’ are there still such polarising views when it comes to health, fitness and weight loss?
THE GOLD STANDARD
The above Authority Nutrition article lists 23 studies demonstrating that a low-carb diet is more beneficial for weight loss than a low fat diet. The article states:
“…Keep in mind that all of these studies are randomized controlled trials, the gold standard of science. All are published in respected, peer-reviewed medical journals.
These studies are scientific evidence, as good as it gets, that low-carb is much more effective than the low-fat diet…”
So of course, as an educated member of the public seeking the gold standard of evidence, based on 23 studies, one could only conclude that science suggests carbs are the enemy and high fat is the solution! But is this really what the evidence says…?
ANALYSING THE STUDIES - AND THEIR LIMITATIONS
When analysing the methodology of these studies, protein intakes were not matched, and the majority did not monitor calorie control in both groups. These two factors alone would make it difficult to draw any conclusions based on the single variables of fat and carb intake across any of these studies, as they were not the only variables manipulated. Here are some further limitations:
Foster GD, et al. (2003) for example controlled calories only in the higher carb group and actually assigned higher protein requirements to the higher fat group.
Gardner CD, et al. (2007) was actually a study comparing several diets, in which the Atkins diet prevails superior. Again, this study actively encourages higher protein intake in accordance with the Atkins diet, and was not calorie or macro nutrient matched with other competing diets.
Hernandez et al. (2010) does not even show any statistical difference in weight loss between the high carb and high fat diets. Instead it focuses on changing triglyceride levels. Should this study really be counted among 23 that prove low carb is more effective for weight loss than low fat?
Samaha FF, et al. (2003) and Daly ME, et al. (2005) were both studies conducted on subjects suffering from type two diabetes. Again, this is a hugely important variable to be considered when trying to apply the results to healthy general populations!
AND WHAT ABOUT THE COUNTER EVIDENCE?
This article uses 23 studies to make it’s point, but forgets to acknowledge the counter evidence. Here are three studies that were available at the time of publication, but were not included as evidence.
(Incidentally - these three studies were calorie and protein matched, and conducted in healthy populations. They show no advantage to weight loss in low carbs vs low fat diets.)
Johnston CS, et al (2006) http://www.ncbi.nlm.nih.gov/pubmed/16685046
‘KLC (ketogenic low-carb) and NLC (non-ketogenic low-carb) diets were equally effective in reducing body weight and insulin resistance, but the KLC diet was associated with several adverse metabolic and emotional effects. The use of ketogenic diets for weight loss is not warranted.’
Soenen S, et al, (2012) http://www.ncbi.nlm.nih.gov/pubmed/22935440
‘Body-weight loss and weight-maintenance depends on the high-protein, but not on the 'low-carb' component of the diet, while it is unrelated to the concomitant fat-content of the diet.’
Golay A, et al (1996) http://www.ncbi.nlm.nih.gov/pubmed/8561057
‘The results of this study showed that it was energy intake, not nutrient composition, that determined weight loss in response to low-energy diets over a short time period.’
IS THERE SUCH THING AS BETTER EVIDENCE?
Below is a systemic review of the topic of low fat vs low carb from 2014. This only includes studies that met strict criteria, removing the possibility for the errors highlighted with many of the 23 studies mentioned previously. The criteria for the systemic review were as follows:
- Used isoenergetic diet comparisons (calories are the same in both diets)
- Used explicit cut-off ranges for macronutrients for treatment and control diets. (equal protein)
- Used interventions were of a diet component alone, or combined interventions were similar (i.e either both or neither groups took part in exercise)
- Used RCT’s only
19 studies met these standards and the results stated:
‘Trials show weight loss in the short-term irrespective of whether the diet is low CHO or balanced in terms of its macronutrient composition. There is probably little or no difference in weight loss and changes in cardiovascular risk factors up to two years of follow-up when overweight and obese adults, with or without type 2 diabetes, are randomised to low CHO diets and isoenergetic balanced weight loss diets.’
Celeste E, et al (2014) http://journals.plos.org/plosone/article?id=10.1371%2Fjournal.pone.0100652
SO CAN YOU TRUST THE GOLD STANDARD?
Sadly, just as politicians come under fire for bending facts to suit their position, the same can be said for cherry picking studies to suit someone’s particular fitness product, method, book or brand. Just because something has a footnote to an academic journal, does not make it fact!
A great example is this bizarre article dismissing the role of calories in weight loss management based on a single 13 year old, widely discredited study; conducted on just 21 participants.
When you see a study tagged on the end of a claim, dig a little deeper. Have a look through the methodology. Check the sample size and date. Read through the funding and competing interests. Hunt for some counter evidence. Is there wider meta-analysis or systemic review of the subject and what was the criteria for inclusion?
PRACTICAL APPLICATION: HIGH CARB vs LOW CARB?
All these studies show that reducing calorie intake will results in weight loss.
In practical application, the variance in success across the studies from different diets confirms what we already observe: Whether physiologically, psychologically or both; clients may respond individually to different diets.
However, when observed on a broad enough scale - such as Johnston BC, et al (2014) meta-analysis of ‘named diet plans’ across 7286 individuals; the results concluded:
‘Significant weight loss was observed with any low-carbohydrate or low-fat diet. Weight loss differences between individual named diets were small. This supports the practice of recommending any diet that a patient will adhere to in order to lose weight.’
Whether, it’s high carb, low carb, or anything else, if your client is happy and can adhere to the deficit long enough to reach their goal - then stick with it!