Chris and Xand are identical twins, which removed any question of genetics from the equation. Along the way, they underwent blood tests and body fat analysis, as well as functional tests looking at cognition function and cycling performance.
In the end, they come to the conclusion that there is no single evil. Instead, the combination of sugar and fat (in processed modern foods) is more likely to induce overeating and influence our weight. I have no argument with their conclusion. However, this conclusion came as moment of enlightenment after 45 minutes of poorly substantiated misinformation, which left most viewers with more questions than answers. I will attempt to shed light on some of these issues below and address the clear anti-fat stance that the show tried to promote.
Before the programme was aired, the Daily Mail published an interview with the twins. The article immediately highlights some potential issues. The identical twins Chris and Xand live on either side of the Atlantic, and their lifestyles have caused significant differences to their physique.
Chris: Having stayed in England, Chris remained the svelter of the two twins at 12 ½ stone (80kg) and started the experiment at 22% body fat. Chris was placed on the high sugar diet.
Xand: Living in the USA, Xand gained weight up to 17 ½ stone (111kg), which at 6ft (183cm) tall, is significantly overweight. Though he had lost some weight before filming, he was still significantly fatter (26.7% body fat) than Chris at the start of the month. Xand then undertook the high fat diet.
We know that previous weight loss and weight gain can significantly hinder future attempts to lose weight due to changes in metabolism and gene expression. As weight variations were a major factor in their experiment, Xand (and the high fat diet) were immediately at a disadvantage. However, they did admit that an experiment of two people was not very scientific. So, for argument's sake, let’s forget this shortcoming and assume that their findings are applicable to the general population.
Xand: In an exaggerated attempt to mimic “sugar-phobic” trends in the USA, Xand starts a high-fat diet, eating literally no carbohydrate. This diet appeared to consist of mostly cheese, cream, steak and processed meats. No fruits, and almost no vegetables.
Chris: As those in the UK tend to lean towards a low-fat diet in the search for health, Chris went on a “high-sugar diet”. Going on the theory that all carbohydrates break down to sugar (particularly glucose), he was allowed everything from sweets, sugar and cereals to fruit and vegetables. He starts to add sugar to everything, whilst keeping his fat intake below 2% of total calories.
Adjudicating over the whole experiment is Dr Richard Mackenzie, an exercise scientist from the University of Westminster. Sensibly, he warns that high intakes of sugar might increase insulin resistance over time, and increase the risk of diabetes. However, worryingly, he also states that saturated fat clogs our arteries and causes heart disease. This begins to show his general lack of knowledge on the topic at hand. Not only has this statement about saturated fat been clearly disproven, the twins themselves even later say that saturated fat is not as bad as we previously might have thought. Dr Mackenzie weighs the twins, analyses their body fat, and will track changes in cholesterol and insulin resistance, which is a marker for potential diabetes.
The Cognitive Function Test
Two weeks into the ordeal, the brothers take part in a test of cognitive function. They are each given $100,000 to play the stock market for the day. At this point, Xand is supposedly running purely on ketones, substances made out of fat that can act as a fuel source for the brain, heart and body when there is no glucose around.
Right from the start, Xand is pictured as listless. He is struggling to concentrate, and compared to Chris, who is full of sugar and bouncing off the walls, he makes less money and “loses” the test.
Let’s ignore that this will involve a lot of luck, and focus on some insight from a cognition expert who administered the test. Professor Robin Kanarek tells the audience that glucose (from carbohydrates) is essential for memory and executive function, which is why Xand struggled on a low-carb diet. It is true that the brain does need some glucose. However, after a few days of a low-carbohydrate diet, it can use ketones for about 70% of its energy needs. The body can then make the small amount of essential glucose required for brain function from the protein in the diet.
Despite what was quoted in the programme, having high levels of ketones (and low levels of sugar) in the blood have also been showed to improve cognition, and even reverse some symptoms of Alzheimer’s disease. Part of the issue here is how early on into the experiment this test was done. Completely removing carbohydrates from the diet, as Xand did, can indeed leave you feeling short of energy until your body adapts to using ketones as an energy source. This can take a few weeks, and Xand clearly still hasn’t recovered from the dietary switch yet. The test would have been much more valid if done at the end of the month, after more time to adapt to using ketones to fuel the brain. It is also possible that, due to the inclusion of large amounts of protein and dairy (which contains the sugar lactose) in his diet, Xand never reaches real ketosis. This would leave him in a low-energy limbo, with just enough sugar to prevent creation of ketones, but too little to fuel his brain or his body properly.
The Hunger Test
Three weeks in, the brothers are brought together to see how their diets affect their hunger. After an overnight fast, both are fed the same number of calories, adhering to the rules of their respective diets. After three hours, both can then eat as much food as they like, and the number of calories is calculated.
Chris eats 50% more calories than Xand, as he was hungrier after a sugary breakfast than Xand was after a plate full of eggs and bacon.
This is a sensible result. We know that fat and protein have greater effects on ghrelin and peptide YY, two key determinants of satiety. Eating a good amount of fat and some protein keeps you fuller for longer, and you then eat less at the next meal.
The Cycling Test
The brothers then undergo a cycling challenge at Box Hill in Surrey, part of the 2012 Olympic road race course. After cycling for an hour at the same speed on stationary bikes to exhaust the muscles, the brothers are each given a small amount of either fat (butter) or sugar (energy gel), before racing to the top of the hill. Chris wins by a long way, and Xand struggles. However, at the end, despite having had no sugar for weeks, Xand’s blood sugar is high. This demonstrated that his body has probably broken down some muscle tissue to fuel the intense final sprint up the hill.
This test was essentially a waste of time. We have known for decades that intense bouts of exercise (such as sprinting up a hill on a bike) are “glycolytic”, and therefore require the energy from carbohydrates to fuel them. Conversely, there is a great deal of evidence that low carbohydrate diets are good for those wishing to maintain strength but lose body fat, and that ketones and fat can also be a more efficient fuels than glucose for very long-distance endurance exercise. As they didn’t test or train the twins in the latter, the winner of this test was always going to be Chris. He was also fitter and lighter to start with.
In addition to this, studies have shown that just the taste of sugar in the mouth is enough to boost performance in a sprint. As there wasn’t enough time to digest the fuel they were given before the sprint, they have inadvertently given Chris a proven boost in his performance. Importantly, a diet high in carbohydrate may be beneficial if intense exercise is part of your daily life (e.g. if you are a professional cyclist). However, for those people, the carbs should still come from whole-food sources rather than from sugar. For the rest of us though, eating the high-sugar diet seen here would likely be very problematic.
After four weeks, the boys return to the lab, and are re-assessed.
Xand has lost 3.5kg in weight - 2kg from muscle and 1.5kg from fat. He is also more insulin resistant, but his cholesterol levels don’t change. He is told that he is now almost in the pre-diabetic range of insulin resistance, and is suitably shocked at what he has done to his body.
Chris has lost 1kg in weight – 0.5kg from fat and 0.5kg from muscle. His insulin response has “improved” as his body adapted to the higher sugar intake. However, he is warned that doing this long-term could still cause diabetes. His cholesterol level also hasn’t changed much.
This is where the message becomes really confused. What is sold as a “victory” for sugar actually ignores a number of very important factors.
Firstly, Xand is told that he lost muscle mass due to his body burning muscle for fuel. However, 2kg is almost exactly the muscle mass you “lose” when you stop eating carbohydrate and use up all your glycogen and associated water (as I’ve explained in this article). It’s perfectly possible that he has lost no muscle at all, and this is all glycogen weight that has been used up, which is completely normal!
Secondly, insulin resistance on a very high-fat and low-carbohydrate diet is well documented and again entirely normal. In somebody who eats a lot of carbohydrate and is diabetic, insulin resistance is a bad thing. It means that the body isn’t able to use up all the carbohydrate in the diet properly, leaving high levels of glucose in the blood. High glucose levels can then damage almost every organ in the body.
However, if you are eating no carbohydrates (as Xand was), the body NEEDS to become insulin resistant in order to stop the muscles and other organs using up the small amount of glucose available, in order to save that glucose for the brain. If you then give this person a sugary drink (as they did in this test), they won’t be able to immediately turn-off this adaptation, and blood sugar levels will rise rapidly. In reality, he almost certainly isn’t “pre-diabetic”, and we are just seeing normal physiology at work. If Xand then re-introduced a healthy amount of carbohydrate to his diet, he probably would regain “normal” insulin function quite quickly.
So at this point, the large negative effects of the high-fat diet are actually completely normal and not as damaging as the audience is told. In fact, Xand even lost more fat than Chris did, which is almost certainly a good thing!
Finally, cholesterol numbers are swept under the carpet. More and more evidence suggests that very high carbohydrate diets will increase triglycerides (not mentioned in the programme), as well as change the subtype of your LDL (“bad” cholesterol), making it more damaging, without actually changing the LDL number itself. As they didn’t test for these things, the high-sugar diet will almost certainly have increased Chris’ risk of cardiovascular disease. This went unnoticed (or perhaps unreported).
The Take-Home Message
As both brothers lost weight, they conclude that the issue clearly isn’t with fat or sugar individually. The brothers then go to look for the root of the problem. They talk to Dr Paul Kenny, a neuroscientist from the Scripps Research Institute, who explains some experiments he did in rats. Much like the brothers, rats which were fed just fat or just sugar gained little weight. However, if given the two in a 50:50 mixture (like cheesecake), rats would gorge themselves into obesity.
The programme summarises that “fad” diets will never work, and that we must tackle obesity by reducing intake of processed foods that combine fat and sugar, and trick our brains into overeating. This is a great conclusion, but the circus that preceded it was entirely unnecessary.
Days before the programme aired, Dr. Aseeem Malhotra tweeted that “Instead of sugar vs fat the debate should be real vs processed food”. Dr. Malhotra is a cardiologist who has become famous in the UK for advising that we reduce our processed carbohydrate intake and increase vegetables and healthy fats. As we clearly knew this already, I question the point of the programme in the first place.
In addition to this, high fat ketogenic diets could in fact be beneficial to people with a number of medical conditions, including diabetes and cancer, but they are clearly not for everyone. Crucially, no modern proponents of a very low carbohydrate diet advise that you completely remove all fruit and vegetables, because they contain some essential nutrients. They also won't suggest that you survive on sausages and cheese, as dairy may prevent the creation of a ketone-based metabolism. This was a completely fabricated high fat “fad diet”, which was used to create good television and seemingly promote the “anti-fat” agenda, which the programme admits is still prevalent in the UK.
We all need to find a healthy diet based around good fats and protein, as well as some nutrients and carbohydrate from fruits and vegetables, whilst removing processed foods. However, the programme that promised to find the answer only muddied the waters, despite a sensible final message.
As I have written this as a comment on the documentary, I haven't compiled a list of references. If you would like evidence to support any particular statements, please say as much in the comments and I will provide suitable articles.