Is low-carb effective for weight loss?

The low-carb diet has not always been positively received, but despite this Health Coach and Author Brendan Reid gave it a shot to support his metabolic health goals. 15 months later and 50 kilograms lighter, his results were astounding, so much so that he published his personal weight loss journey in the book ‘The Fat Ginger Nerd.’ But the lingering question remained, why is the low-carb diet not promoted by the Ministry of Health and instead what are we being told to eat and why, to stay healthy? Brendan delves into New Zealand’s Dietary Guidelines and the very research they are based on for metabolic health.

Watch Brendon Reid’s full talk on Low-Carb for Weight Loss from The Future of Medicine Conference 2022 below.



NZ Dietary Guidelines vs Low Carb for Weight Loss 

New Zealand’s dietary guidelines were last updated end of 2020. For those unfamiliar, the broad messages coming out of these guidelines emphasise the importance of various things like fruits, vegetables, grains, and lean meat, while saturated fat continues to be seen as some sort of nutritional devil. Clearly, there are several incompatibilities with what the standard guidelines might be promoting, compared to what a typical low-carb diet might perhaps look like. 

There is not necessarily any direct reference to low carb specifically within the guidelines themselves, but where we do see a reference to low carb in Ministry of Health policy is in another document that sits on the website just beside the dietary guidelines. This comes from a document of topical questions and answers published by the Ministry back in 2015. I couldn’t help catch my eye when I found this because it asks, is a low-carb diet the best way to lose weight? And so the short answer on the part of the Ministry is well, no. 

They say it’s all about the energy in the diet, that’s what’s important. Not so much about what types of foods that energy comes from. So the emphasis here is very much all about food quantity with very little regard, recognition or even awareness of any concept around the notion of food quality and nutrients. 

Let’s hold that thought for a moment now while we take a look at some of the science used by the Ministry of Health. There is a meta-analysis of randomised controlled trials looking at a range of low-carb and low-fat diets on the subject of weight loss. The trials ran for six months and the statistics show that weight loss tends to increase as fat and protein are proportionally increased in the diet. And so all of what we’re seeing is very much at odds with the Ministry’s position statement on weight loss, it is not to say that energy doesn’t matter, it certainly does but when it comes to weight loss, there’s more to it, it would seem, than just energy balance alone. 

So the next part of what the Ministry says is they do sort of acknowledge in some way that people can lose some weight on some low-carb diets sometimes, but this happens with other diets as well. And sure, I am happy to acknowledge, accept, and indeed celebrate the fact that different people can and do lose weight on a range of dietary patterns, plenty of evidence out there to support this. 

But there’s another example of a meta-analysis of randomized controlled trials taken from a range of studies and grouped into five named dietary patterns and then compared against each other. It provides a matrix of findings and the numbers show that low carb does appear still to be the most effective option for weight loss after six months. After 12 months there isn’t so much of a clear number one, as there is at least a clear top two. You’ve got low carb and low fat, which are both your clear standouts. 

And indeed the conclusion coming out of this review says something to the effect that this supports the practice of recommending any diet that a patient will adhere to in order to lose weight, which one would think on the basis of these numbers, at the very least perhaps consider including low carb as a viable option. But alas, the Ministry of Health is still saying there’s just no evidence of the long-term benefits or safety of such diets. 

And so immediately I read that and I think, what do they mean exactly by long term? I know enough that as your gold standard of evidence, your RCTs, how long-term can we get in this context? We’ve seen numbers for six months. We’ve seen numbers for 12 months. Can we go further than that? Turns out we can. There’s another newer meta-analysis, comparing a range of low-carb, low-fat diets for weight loss trials that ran for a full two years. And once again while we see that, we can’t necessarily go as far as to say low carb is your clear winner in this regard, it is by no means a clear loser either. There’s still enough here in my mind to suggest that low carb could still be considered at least a viable option for weight loss for up to two years.

And yet, based on all the current evidence, the Ministry of Health does not recommend low-carb diets for weight loss. So, given the evidence, and my own experience makes me just a tiny little bit biased on this particular subject, I can’t help but be confused about what the Ministry is saying here. I want to understand a bit more about their point of view. Where are they coming from here? What is the basis for the Ministry of Health’s claim of a lack of evidence on low carb for weight loss? So, what this led me to do, is start taking a closer look at some of the evidence for the eating body weight statements that the Ministry uses in putting their guidelines together.

It turns out they’ve got four key evidence sources that the Ministry looks to interpret, with the key review conducted by the USDA back in 2014, that was dealing with dietary patterns and body weight outcomes. This was in essence to understand the relationship between what we eat and what we weigh. So in response to each of these questions, the committee conducted a range of searches of the scientific literature, and then they subject each of their findings to a range of eligibility criteria. Paying particular attention to the last two of their three criteria here, in essence, the committee is saying that they are only interested in studies on healthy people. 

Therefore studies on any sort of population group dealing with any sort of chronic health condition or any sort of disease diagnosis are not going to be considered as part of this review. So consider what that might mean for a lot of the low-carb science that we know is out there, with the understanding that many of these studies tend to be conducted on people with chronic health conditions. Conditions like obesity, type 2 diabetes, high blood pressure, and so on. Things that we know on the one hand are caused by a poor diet, and yet at the same time, they could also quite reasonably be counted as disease diagnoses. Well, here’s an example of some of your eligibility criteria that might go some way to explain why a lot of that low-carb science is not necessarily going to be incorporated into the findings of this review.

Just one of a number of examples is that there is actually a list of the dietary patterns that the committee searched for in looking to answer their questions. They’ve gone looking for evidence on the Mediterranean diet, the DASH diet, vegan, vegetarian and so on. But there is no inclusion of low carb, keto, paleo or carnivore. They’re just not there. 

So regardless of any potential issues around the eligibility criteria, it turns out that ultimately the fundamental reason why practically no low-carb science was featured in the findings of this section of this review, at all, is because the committee never even actually searched for any of that science in the first place. And so once I realised that this is what I was looking at here, my mind is just completely blown away.

It therefore, comes as no surprise to learn that the actual findings in the end of this review were very much a reflection of the various commonalities of the various dietary patterns that the committee did search for. So naturally, the conclusions here are going to be all about the importance of your fruits, your vegetables, your grains, your lean meat. If any, saturated fat is still the devil. 

And at this point, the flow of information becomes very clear because this is all completely 100% consistent with what we see in the messaging in New Zealand dietary guidelines themselves. And so when we come all the way back to our original position statement, we can see what the Ministry is saying, with perhaps a better understanding or appreciation for how they’re arriving at these particular conclusions. 

So, some food for thought, the statement that the Ministry of Health makes on the subject of low carb for weight loss is actually dated 2015, but it’s still being used today in 2022. While a lot of the evidence we see is actually newer than that, is it worth taking a look at this question, if low-carb was the best way to lose weight or best for whom? What if instead we simply asked if low carb was maybe just a viable option for some people to lose weight? Would the answer to that question perhaps be a little bit different? We can go on and on about the burden of proof and all the issues of methodological inconsistencies. But, to touch on the point I was making earlier about how the eligibility criteria was only really just dealing specifically with healthy people only. So it would seem, that one could make the argument that the effective scope of New Zealand’s guidelines themselves is only limited to metabolically healthy people. 

So why, therefore, would anyone look to advise people to simply follow the dietary guidelines in order to lose weight, for example, if those guidelines do not necessarily take into consideration the best available evidence on the very condition from which these people are suffering? Do we perhaps need to be a bit more transparent about the effective scope of our dietary guidelines as they currently stand? Do we perhaps need to look at a second parallel set of guidelines, for example, for people with chronic metabolic disease with weight to lose? 

Would it interest you to know that such a document in New Zealand does, in fact, exist called ‘Clinical guidelines for weight management in New Zealand adults’. When I found this, I was really excited, I thought, if only something like this had been around when I was struggling all those years ago. But when I had a look and see what it says, the very first bullet point at the top of the list says to eat less. Particularly of energy-dense food!

So right away we are back to square one with the line about energy balance being the be-all and end-all when it comes to weight loss. What else do we see? When we have a look at the rest of this list of recommendations there is fruits, vegetables, grains, lean meat, and saturated fat is still the devil.

A lot of this is sounding pretty familiar at this point, right? That’s basically because they’re directing these poor people straight back, in effect, to the standard dietary guidelines.

No further comment. I rest my case.


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