The global obesity epidemic is growing at a staggering rate and shows no sign of slowing; 1 in 3 people in the UK will be obese by 2034 and 1 in 10 will develop Type 2 diabetes.
Prevention remains the most effective treatment strategy for addressing this unprecedented public health catastrophe. The solution requires changes in health policy and eating behaviours. But, one scientific question remains unanswered: why are some of us susceptible to weight gain while others can eat anything with impunity?
Do our genes make us fat?
If you read the popular press, you could be forgiven for thinking that the obesity epidemic is largely the result of our genes.
Our genes are part of the problem, but it doesn't take a rocket powered obesity scientist to work out that our lifestyle and eating habits play an important role in determining our weight. Just look at the amazing speed that the obesity epidemic has swept the country, that is not explained by genetics.
Gut feeling about obesity
A recent discovery has been that the bacteria within our gut play an important role in determining our weight. Your "genome" (all the genes that code and make you) is dwarfed by the gut "microbiome" (the microbial genes that reside within your gut) - a massive, highly individualised engine essential to your health.
Much like any other ecosystem, diversity is an important biomarker for health, and research suggests that obese people lose some of the diversity in their intestinal ecosystem. Obese individuals possess different bacteria to lean people that are very efficient at harvesting energy from their diet.
What does your microbiome do?
Your gut bacteria have a staggeringly large armory of signaling pathways. They metabolise your food, your medicines and environmental toxins, they provide you with essential nutrients and they educate and modulate your immune system. You and your bugs are entirely co-dependent on each other for your mutual health.
But the microbiome may also control your eating behavior and feelings of satiety and hunger. The "Gut-brain" axis could therefore explain why some people keep eating when they should really stop.5 It may also explain changes in feelings of anxiety or depression.
Can you change your microbiome to lose weight?
It maybe that antibiotics, probiotics and prebiotics treatments have a role, but as of yet, we are lacking really good evidence for their use. Even faecal transplantation has been suggested, but this is not a treatment that is acceptable and it carries real risks. Interestingly, some patients treated with faecal transplantation have reported becoming obese after the therapy.6
It is also worth remembering that this is a complex science. Human genes do help determine which bugs you host in your gut and how you will respond to some dietary components. Secondly, we have yet to really establish the cause and effect for the gut microbiome in obesity. Thirdly, many of the experiments on the microbiome have been done in animals, and these are not representative of the human gut. Fourthly, it may be what happens in very early life that is really critical.
For now, if you really want to lose weight by changing your microbiome, then you still need a balanced, low-calorie diet used in combination with a planned exercise programme. I am afraid there are no short cuts!
What does your microbiome want to eat?
The microbiome is so personalised it is difficult to recommend a single diet that will benefit everyone, however here are some top tips:
• Your colonic gut bacteria really like a diet that is high in complex fibres, so choose wholegrain starches when possible and enjoy plenty of fruit and vegetables (at least 5 a day!). You really need 50g per day for improved colonic health (way more than the recommended daily allowance).
• You do need some protein-rich foods such as white meat, fish, eggs, beans and non-dairy sources of protein, such as nuts and pulses. Avoid processed meats and red meat.
• You can have milk and dairy, but choose reduced fat versions.
• Be cautious of 'microbiome based diets' for weight loss that encourage fermented foods, probiotics and organic produce, as there is not always evidence that they will help you lose weight and they certainly won't work unless you take them as part of a healthy diet.
If in doubt, seek the advice of your GP or a dietician.
What's next for the microbiome?
In the last decade, we have taken the few first steps into this new area of science and its importance is only just being understood. In the future, we are very likely to see personalised treatments that target the microbiome. For now though, the obesity epidemic rolls on...