BBC Horizon’s Sugar Vs Fat: A Constructive & Comprehensive Review

It’s Wednesday night at 10pm and it’s been a full on day of coaching my diet and exercise class in East London, as well as catching up over a public Google Hangout with some online clients known as the “Diet Dunces”. My phone vibrates, followed by my tablet making a notification sound, nothing unusual there but this goes on for a further 30 minutes about once every 90 seconds and when I wake up the following morning I have 33 messages in regard to a documentary on BBC’s Horizon called Sugar vs Fat from clients, friends and colleagues. After sifting through these 33 messages of rather worrying queries I started to wonder what on Earth could they have said in this documentary to warrant such questions?

If you didn’t see it last week on BBC’s Horizon programme twin doctors Chris and Xand Van Tulleken went on a month long high-sugar and high-fat diet respectively to see which is worse, sugar or fat. Originally I wanted to get a review up as soon as possible to strike whilst the iron was hot but then I thought I’m going to sleep on it, take my time and process all the information in the programme over a week in an attempt to be as constructive and comprehensive as one can be in my review process…


The programme starts by setting the scene, saying that traditionally fat has been the bad guy in Britain and that over in America it’s sugar that’s under attack. However, we know from BBC’s very own documentary The Men Who Made Us Fat in August 2013, that it was Britain who was originally concerned that sugar was harmful in certain quantities that are easily met on a daily basis through the research of Dr. John Yudkin and his book Pure, White & Deadly in 1972…which is actually continued today by his son Michael who is Professor of Biochemistry at Oxford University. I understand the need to set up a “battle” of sorts in docu-tainment but this is not even close to the reality with Action On Sugar launching last month with a multitude of professors, doctors and experts supporting it.

The Diets

They show the 2 different diets on a kitchen table with nutritionist Amanda Ursell. First up the high-sugar diet is presented to Chris with bread, pasta, potato, fruit, vegetables, fizzy drink and sugary snacks, pretty much my high carb low fat fake food diet. Not much is mentioned about any benefits or side effects but Chris did say at one point “none of these foods have fat” which is incorrect as the majority of them do have some amount of fat as it is essential to most living organisms on the planet, not sure why the nutritionist didn’t correct him or they just didn’t keep that bit in the editing process. I know that seems like nit picking but this is the BBC, and Horizon at that, which should be held up to the up most accuracy of information.

The camera then pans over to Xand and his high-fat diet who is shown bacon, eggs, meat, cheese, double cream and some vegetables, which for some reason weren’t put on that side of the table despite it being on the diet. Xand then goes on to explain that his problem is that he won’t have a poo for a month, which can be a legitimate problem when changing your diet from high carb to low carb as your gut adapts to the different food but this doesn’t happen to the majority and isn’t necessarily about the fibre. In September 2001 there was a systematic review of 20 studies which concluded “There is not strong or consistent evidence for the effectiveness of treating constipation in institution-dwelling older adults with dietary fiber” then in September 2012 a study of 63 people with chronic constipation concluded “constipation and its associated symptoms can be effectively reduced by stopping or even lowering the intake of dietary fiber.” so basically the jury is still out on whether it’s always appropriate to recommend dietary fibre to reduce constipation. On a side note it’s more than easy to design a low carb high fat diet plan that contains enough fibre through vegetables and nuts, often people end up increasing the amount of vegetables they eat when shifting to a low carb high fat diet to “bulk” the meals. See my FAKE FOOD REHAB diet as a starting point.

The nutritionist then goes on to say that on top of that you will get bad breath, which again is a common concern raised by people but really a matter of opinion as when you move to a high-fat diet you usually go into ketosis more often which makes your breath smell like ripe fruit but this is not to be confused with halitosis. When they went through the high-sugar diet they didn’t mention the fact that it is well documented that a high-sugar diet is exceedingly bad for oral hygiene causing actual halitosis by the sugar feeding bacteria in your mouth causing plaque to build up.

At the end of this segment they go on to say that they can eat as much as you want, which is what I usually recommend to my clients but in an experiment it is important to track everything to be able to extrapolate as much information from your findings. I would have liked to have seen equal calories consumed to make a true comparison between the 2 diets or at least have their calories tracked all the way through the programme to be able to make a comparison and examine the energy balance hypothesis of obesity. As it has been shown numerous times in many studies that a low carb high fat diet is superior in weight loss despite similar or more calories being consumed. Also, it would be interesting to see if the nutritionist made sure that cheese was limited as to make sure that Xand didn’t come out of ketosis due to the carbohydrates in cheese in the form of lactose. If anyone from the programme would like to share this information please do.

My main concern with this part of the programme was that they presented the high-fat diet, which contained all real food, to be worse than the high-sugar diet, which did contain real food but also a fair amount of fake foods and didn’t even mention any detrimental effects from it. I feel it would have been more fair to have a nutritionist for each twin, one that’s pro-sugar and another that’s pro-fat. This way both diets would have had there corners fought equally.

Brain Function

The twins tried to test how well their brains worked on their different diets by trading on a pretend stock exchange with £100,000 each, which is great entertainment as Chris lives in London and Xand lives in New York but not really a fair test to show any improvement or detriment to their levels of cognition. In this segment of the programme it’s set up from the start that Xand on his high-fat diet is going to have a hard time with this task and he does, as he loses to Chris on the high-sugar diet and in all honesty I’m not surprised. If you put some one who has been eating a conventional high carb diet on to a high fat diet and ask them to perform a difficult cognitive task that they’re completely new to after 2 weeks from making the switch then they’re going to have problems until their body’s become used to running on ketones, the wash out period is usually 6 weeks. Perhaps we should have put Xand on a high fat diet for 35 years then done the test. I hope that most people didn’t take this bit seriously but alongside the test they had Dr. Robin Kanarek from Tufts University explaining that glucose is “the primary fuel source for the brain and the best fuel for the brain” which is an interesting statement. I would say that glucose is the primary fuel source if it’s available, meaning that you’re brain and body will burn it off first before moving on to ketones, but it certainly isn’t the best fuel for the brain. In fact high glucose levels are now associated with risk of dementia and a ketogenic diet is currently the best treatment we have for neurological diseases such as child epilepsy and alzheimers, and conceivably the best preventative measure for them to, again something that isn’t mentioned even though this is well known through the medical community. On a personal level I found when I originally moved to a low carb high fat diet my cognition improved and recently whilst I’ve been on my latest high carb low fat vegan diet my level of cognition has declined. Here’s a great TED talk from Dr. D’Agostino, Assistant Professor of Molecular Pharmacology & Physiology at the University of South Florida College Of Medicine explaining about how ketogenic diets work for neurological diseases.

Chris on his high-sugar diet does do better and as the doctor mentions in her commentary at least in the short term he will be able to function better due to the amount of glucose he is taking on board, not sure why they didn’t go on to mention what would happen in the long term? It would have been nice to have a balance with the down side of too much sugar and it’s implications with alzhemiers in accordance with neurologist Dr. David Permlmutter.

Finally, after this segment Xand meets up with Professor Robert Lustig from the University of California to talk about sugar and it’s detrimental effects on the body. At the end of their discussion Xand dismisses Prof. Lustig’s science saying that he is not convinced as generally the studies have unrealistic amounts of fructose. One of which is a study of 175 countries showing that even 150 k/cals a day of sugar, just over a can of cola, increases your risk of type 2 diabetes. Of course we should be sceptical especially when it comes to observational studies but I would have liked Horizon to present the data quickly to the audience to make up their own mind instead of just dismissing it or even have the science director of Action On Sugar and Smash The Fat Ambassador Dr. Aseem Malhtora say his piece.

My main concern with this segment was that it was not a fair test to begin with, as Xand would not have been fully fat adapted and as you will see from the exercise section it’s questionable as to whether he went into optimal ketosis for normal function anyway.


Its now halfway through their experiment and the twins decide to do an exercise test. They recruit head of nutrition from Team Sky, Nigel Mitchell, to put them through their paces on bikes to see which is better for exercise sugar or fat? First things first, the guys hadn’t exercised in 2 weeks and secondly we know that it takes people 6 weeks to fully appreciate the benefits of ketosis when it comes to exercise. Anyway, they start off by doing an hour of stationary cycling and measuring their blood glucose and ketone levels. After this they head to the infamous box hill, at least in cycling circles, and before they head up the hill they each have some food in respect of their diets. Chris has an energy gel, packed full of sugar, and Xand has some butter, packed full of fat. The problem here is that if Nigel Mitchell knew what he was talking about in regards to a high-fat diet for exercise he’d know that butter, mainly short chain fatty acids, isn’t the best source of fat for instant energy but a spoon full of coconut oil, mainly medium chain fatty acids, is as it can be used as instant energy levelling the playing field a little for the climb, even though it’s not fair from the start. Again I would of liked to have seen an expert who was pro-sugar for Chris, Nigel Mitchell, and an expert who pro-fat for exercise, Professor of Exercise & Sports Science at Cape Town University Tim Noakes or team doctor for the Australian cricket team Peter Brukner.

The lads head up the hill, and again unsurprisingly Xand on his high-fat diet loses the climb. Afterwards Nigel Mitchell takes their blood glucose levels again to see what happened. Chris on his high-sugar diet has a blood glucose level of 7.1 mmol/L compared to his 2.7 mmol/L after the hour of stationary cycling, which is because he just ingested an energy gel which would have pretty much just been glucose. Xand on his high-fat diet has a blood glucose level of 5.1 mmol/L compared to his 3.3 mmol/L after the of cycling. Nigel says that this is because his body would be making glucose from muscle, which actually isn’t correct as if there is a presence of dietary protein your body will make glucose from that first and if I remember correctly he ate a few sticks of butter just before he started? Also, as long as he eats an appropriate amount of protein after this cycle there certainly won’t be any muscle loss of any kind. Finally, Xand rightly says that he “feels quite rubbish” which again is because he isn’t properly fat adapted yet and this is shown through the ketone levels that were on the white board they had but did not discuss? It showed that Xand was at 0.4 mmol/L before the cycling and 0.5 mmol/L after the cycling which is actually normal levels of ketones for the average Joe walking on the street. To be properly fat adapted he should have been at least over 0.6 mmol/L and ideally he should have been around 1.5 mmol/L meaning that at this time he probably had too much protein or even carbohydrate, most probably in the form of lactose from cheese, in his diet to go into what many of the leading experts in this field call nutritional ketosis. One of which is Dr. Stephen Phinney who has been at the forefront of low carb diets for performance along with Associate Professor of Kinesiology at the University of Connecticut Dr. Jeff Volek.

My main concern with this segment was that they said that on the high-fat diet Xand was making glucose from his muscle causing loss of muscle and not from dietary protein, which he would have been doing. This is worrying people who are on low carb high fat diets that they are losing muscle when quite the opposite is happening. I would like explanations from the twin doctors and Nigel Mitchell for what I see as a massive oversight in how the human body works?

Weight Loss

Both twins lost weight over the month but Chris with on his high-sugar diet losing 1kg (0.5kg of body fat and 0.5kg of fat-free mass) and Xand on his high-fat diet losing 3.5kg (1.5kg of body fat and 2kg of fat-free mass). Dr. Richard MacKenzie from the University of Westminster measured the lads weight using a BodPod and his conclusions on their weight loss are honestly quite astounding. He says that their loss in fat-free mass was from muscle, following up by saying we have to look at this in detail and that his loses are unhealthy? As someone who uses a BodPod regularly I know that it can only measure body fat with a relative degree of accuracy. The rest is fat-free mass, so everything apart from body fat including organs, bone, muscle, water and glycogen. I would like an explanation as to why Dr. MacKenzie said this as I’m sure he knows their is a massive difference? Both of their weight loss in fat-free mass would most probably not have been from muscle but from water and in Xand’s case glycogen as well which can equate to drum roll please…2kg. The only sure fire way would have been to use a DEXA scan, but perhaps that would have shown what really happened in their weight loses and health. Finally, Dr. MacKenzie dresses it up even more saying that because Xand on his high-fat diet has lost “muscle”, which he wouldn’t have, he is more likely to have a poor life expectancy! This is pure scare mongering of the high-fat diet as this isn’t directed to Chris on his high-sugar diet either who also apparently lost muscle mass too?

My main concern with this segment was that not 1 out of 3 doctors stood up to the producers of this programme to say, “what we’re saying here isn’t entirely accurate, the loss in fat-free mass was most probably not from muscle but from water and glycogen”. I would like full explanations from all of them for this lack of scientific integrity!

Blood Tests

In the final segment of results from their experiment they look at their blood work. Firstly cholesterol which they said came out with little or no change in either of them. This felt like it was skimmed over with detail as we know from many clinical trials that when people go on a low carb high fat diet their cholesterol profile improves, especially their triglycerides or fat in the blood which usually plummet (a good thing). If anyone from the programme is reading this I would love to see their numbers.

Next up was their insulin levels using an oral glucose tolerance test (OGTT), where they both drink of pure glucose. This part of the programme confused me and it felt a little awkward as it wasn’t entirely clear which results they were talking about, the pre-OGTT or post-OGTT? Dr. MacKenzie starts off with Chris on the high-sugar diet saying that he has become a better producer of insulin, meaning that he produces more insulin to bring down his blood glucose levels. Dr. MacKenzie says that it’s good in the short term it’s good and that in the long term it might be…it might be…it might be a problem. When Dr. MacKenzie was saying this it felt like he was having trouble with the conviction of his statement as this can be a huge problem, it’s called type 2 diabetes, cancer, heart disease and dementia! It was almost like during this analysis of results they didn’t want to say anything bad about the high-sugar diet, but it felt like it was on the tip of their tongues? They move on to Xand’s results and Dr. Mackenzie says it’s bad news. Xand started out with blood glucose levels of 5.1 mmol/L, which is well with in the healthy range and now after a month it’s at 5.9 mmol/L which is…still within the healthy range. As I mentioned earlier it wasn’t clear which results they were talking about pre or post OGTT and also it would have been nice to hear what Chris’s results were instead of just focusing on how bad Xand’s were. Which they were not, as there is a 20% margin of error in blood glucose tests. Also, if this was post-OGTT then a healthy range is <7.8 mmol/L, I would have liked clarification on how the tests were conducted?

My main concern with this segment was that all the focus was on how poor Xand’s results were, with no balance about the detrimental effects of Chris’s results, and that he needs to stop this diet immediately to avoid becoming type 2 diabetic when every study is showing that a low carb high fat diet is improving all bio-markers for type 2 diabetes?


My final thoughts on this docu-tainment programme was that I agree with their final thoughts that processed food should be avoided, but how they framed their point and focused the majority of the show telling the viewer that a high-fat diet is the worst thing that you can do was unscientific and not representative of where the current science is heading. There are many leading scientists who are advocates of low carb high fat diets from well known academic institutions and from the private sector…

Prof. Tim Noakes
Prof. Helen Cross
Prof. Grant Schofield
Associate Prof. Jeff Volek
Dr. Andreas Eenfeldt
Dr. Stephen Phinney
Dr. Jay Wortman
Dr. Eric Westman

…just to name a few. I would have liked to of seen the programme at least consult some these leading experts in ketogenic diets to design Xand’s diet and also to have guided them through the month as well as showing them the evidence that they skimmed over to make a point that sits on the fence, with a slight emphasis that high-fat diets are going to kill you, and goes along the same old advice of “eat in moderation” which doesn’t really give the viewer anything productive to walk away with. If you would like a dietary system that is proven to work through the work of the above professors and doctors please download The Lifestyle Diary for free @

Let me know your thoughts below!