Eat Healthily, Consider Using Time Restricted Eating, and Prioritise Building a Strong Gut Microbiome


Don't worry about particular diets or restrictions (unless they are for personal moral reasons). Instead, focus on eating real food and avoiding processed foods and refined sugars. If suitable for you, time-restricted eating can be an effective way to manage your insulin levels and control your weight. Feed the trillions of good bacteria living inside you so that they can nourish and protect you.

Want to look at the science later but, right now, you are just interested in some actions to take?

Cut out all ultra-processed foods and refined sugars. Aim to prepare and cook your own meals from ingredients you have chosen.
If you eat meat, choose grass-fed and grass-finished beef, pasture-raised poultry and wild caught, sustainable fish.
For meat and vegetables, choose organic produce.
If time-restricted eating is safe for you (see below) then reduce the window of hours in the day when you are consuming food to improve your metabolic health, lose weight and reduce visceral fat.
Deliberately include pre-biotics (e.g. fibre) and pro-biotics (healthy bacteria) in your diet to improve the health of your gut microbiome for a wide range of health benefits.

Why should you focus more on eating real food than on any particular diet?

What you eat, how much you eat, and when you eat has a profound impact on your health now, your healthspan and longevity. Yet this is the area, perhaps more than any other, is full of contradictory advice, highly specific diets and ‘wars’ between opposing camps.

Let’s just take a quick look at some of the main diets you might bump into:

  • Paleo: Eat only what would have been available to our hunter-gatherer ancestors. This diet has a focus on lean meats, fish, fruits, vegetables, nuts, and seeds. The Paleo diet excludes grains (wheat, oats, rice), legumes (beans, lentils), dairy products, refined sugar, and processed foods. Its aim is to eliminate modern agricultural foods, reduce inflammation and align with our evolutionary biology.
  • Ketogenic: Follow a diet very low in carbohydrate and high in fats and protein. This diet has a focus on healthy fats (olive oil, avocado), fatty fish, meat, eggs, and non-starchy vegetables (leafy greens). The ketogenic diet excludes sugar, grains, starchy vegetables (potatoes, corn), and most fruits. Its primary aim is to force the body into ketosis, turning it into a highly efficient fat-burning machine for weight loss, steady energy and sharper cognition.
  • Mediterranean: Eat following the traditional patterns of countries bordering the Mediterranean Sea (like Greece and southern Italy). It is widely regarded by medical science as one of the healthiest long-term dietary patterns. This diet is abundant in vegetables, fruits, whole grains, beans, nuts, seeds, a heavy emphasis on extra virgin olive oil, and moderate amounts of fish and poultry. The Mediterranean diet excludes processed red meats, refined grains, and ultra-processed foods. This diet is held to be sustainable, rich in polyphenols and monounsaturated fats, and heavily backed by clinical evidence for longevity and heart health.
  • Vegan/Plant-Based/Vegetarian Follow a diet that either minimises or entirely excludes animal products, focusing instead on foods derived from plants. Vegetarians exclude meat and fish but often include dairy and eggs. Vegans exclude all animal derivatives entirely, whereas plant-based allows for minimal, occasional animal intake. This diet includes vegetables, fruits, whole grains, legumes, nuts, seeds, tofu, and tempeh. It excludes meat, poultry, seafood, and (for vegans) dairy, eggs, and honey. The aim of this diet is to lower cardiovascular risk, optimise environmental sustainability, and boost gut microbiome diversity via fibre.
  • Carnivore: An elimination diet that sits at the exact opposite end of the spectrum from veganism. It involves eating exclusively animal products. This diet is dominated by beef, steak, organ meats, fish, eggs, and sometimes heavy dairy and excludes every single plant food i.e. no vegetables, no fruit, no grains, no nuts, no seeds, and no fibre. Its claim is to eliminate all potential plant toxins and anti-nutrients, acting as the ultimate elimination diet for severe autoimmune or gut issues.

If you look at the list above and read about these diets, you’ll soon notice a fierce tribal war. The Carnivore diet bans all plants. The Vegan diet bans all animals. The Keto diet fears a sweet potato, while the Paleo diet fears a bowl of lentils! But if you strip away the dogma, the healthiest variations of almost all these diets share one undeniable foundation: they eliminate ultra-processed food/sugar and emphasise real, single-ingredient, nutrient-dense fuel.

My own personal opinion is that the Mediterranean diet is probably the best on the basis that it includes a good variety of food sources, is sustainable (people can easily keep to it) and has been extensively studied in relation to its cardiovascular benefits. The ketogenic diet can be hard for people to stick to, and I think you can achieve many of its benefits by using time-restricted eating and fasting (see later). My own choice for ethical reasons is plant-based (with my compromise being some cheese occasionally as a treat and my fish-based Omega3 supplement). I think the Carnivore diet is very extreme, and I simply cannot see how you can sustain a healthy gut microbiome on that diet (see later).



I would urge you to focus on the following characteristics of your food rather than a specific diet:
  • Above all other things, avoid all ultra-processed foods [1]. Be suspicious if it comes wrapped in plastic or is in a box or a packet. Be especially suspicious if it has a long list of ingredients.
  • Avoid refined sugars, sweets, cakes, etc. to avoid spiking your blood sugar and metabolic disorder [2] [3].
  • Focus on slower release, whole-grain carbohydrates and try to combine your carbohydrate with some fibre (eg a salad).
  • Check ingredients carefully and look out for sugar featuring anywhere early on.
  • Whether you are eating meat or vegetables – try and eat as much as possible from organic sources.
  • Ensure you are getting enough fibre to support your gut microbiome.
  • If you eat beef, aim for a source that has been grass-fed and grass-finished.
  • If you eat fish, try and choose species not on the endangered lists and prefer wild caught over farmed.
  • If you eat poultry, look for pasture-raised.
  • If you eat meat, avoid preserved meats like sausages and bacon. The nitrates and nitrites used in the production of these foods convert to carcinogenic chemicals when the meat is cooked [4]. Stick to beef, good quality fish and poultry.
  • In all animal products look for trustworthy ethical logos and marks. These products will be more likely to meet those organic and livestock criteria for a healthy food source.
  • With your fruit and vegetables: “eat the rainbow”. Look for a good diversity of reds, yellows, oranges and especially make sure you are getting some purples as well in there.
  • If you don’t already, try to shift your meal preparation from ‘heating food already prepared for you’ to ‘cooking a meal from various ingredients you have bought individually’. There is no easier way to skip ultra-processed foods than simply processing your own food!


With my thoughts on what to eat out of the way, let’s turn our attention to when/how often to eat:

Why could you consider time restricted eating and even fasting?

The essence of time-restricted eating is to eat roughly the same amount of calories as you do normally but to reduce the window of time in the day when they are consumed (and to avoid snacking between meals).

While time-restricted eating and longer fasts can be a useful tool for metabolic control, they are not suitable for everyone. Please consult your doctor before changing your eating patterns. Specific concerns (but note this is not an exhaustive list) would be:
  • You are a medicated diabetic
  • You are pregnant or breastfeeding
  • You have a history of eating disorders
  • You are underweight
  • You are a child

There are many patterns to follow, so you can experiment with what works for you. For example, you could skip breakfast, eat lunch around midday and dinner around 6pm. You are thus only eating for around 6hrs of the day and fasting for 18hrs of the day (which is referred to as an 18:6 split).

Rather than launching straight in with something like an 18:6 split, you might want to build up slowly by starting with perhaps a 12 hr feeding window and reducing that over time. Although there are all sorts of patterns and ratios you could use, try to avoid eating close to your bedtime, leaving at least 3 hrs if not more between your last meal and sleep. You can read more about eating and sleep in Big 10 #3.

What are the benefits of time-restricted eating?

  • Metabolic health: Throughout your fasting period you are avoiding elevating your blood glucose (and thus insulin), which can help to combat high-insulin levels, inflammation, and protect against type 2 diabetes. You can read more about blood glucose monitoring and insulin in Big 10 #1 [5] [6]
  • Visceral fat reduction: Visceral fat is the ‘hidden’ fat that builds up around your organs and is particularly dangerous when it comes to inflammation and metabolic health. In your fasting period your body will draw down on this visceral fat and, over time, help to reduce it to a healthier level [8]. You can read more about visceral fat in Big 10 #6
  • Weight loss: Although you are not attempting to restrict your calories, a natural function of restricting the feeding window is that it can be hard to consume the same amount you always did. In addition, eating real foods which are high in fibre, good fats, and protein (and low in refined sugar) will help you feel fuller and experience more even blood sugar levels. Both of these will also help with weight loss over time, and you may well find that time-restricted eating is less uncomfortable (and more sustainable in the long term) than calorie restriction [9] [10].
  • Achieving ketosis: Straight after your last meal your body is in a fed state, insulin levels are elevated, and your cells are burning glucose. As you move deeper into your fasting window, blood glucose levels begin to drop and your pancreas will signal to your liver (via the hormone glucagon) to break down stored glycogen to release more glucose. Towards the end of the fasting period (around 16 hours, but this can vary hugely person to person and depending on what your last meal was), all the ’easy’ sugar is gone, and the body flips to breaking down stored fats (lipolysis). The liver converts these fats into ketone bodies. These ketone bodies (e.g Beta-hydroxybutyrate - often abbreviated to BHB) can cross the blood-brain barrier and are a very efficient source of energy. Some people report feeling more alert and focused when in ketosis, and this (along with metabolic stability, reduced inflammation and possibly even longevity and cell renewal) is one of the benefits that advocates of a ketogenic diet espouse. Some people find a ketogenic diet hard to stick to in the long term, and time-restricted eating can be a way to ‘dip your toes’ into ketosis daily. If you are interested in finding out if you are actually achieving ketosis towards the end of your fasting window, you might like to use a blood ketone monitor such as Keto Mojo or even a continuous ketone monitor like SiBio. Ignore the urine test strips as they are generally not accurate and are more of a gimmick. To be honest, on a 16-hour or 18-hour fasting window you may not get into ketosis (or if you do, not to a significant level or not for very long) and, if this interests you, then you might want to intermittently add in a longer fasting window.

Fasting for longer periods of time

If time-restricted eating works well for you and you feel well on it, then you could also try adding in occasional longer fasts (e.g. a 48 hr fast once a fortnight). A longer fast will intensify the benefits listed above, and you are much more likely to achieve a high level of ketosis.

As for the time-restricted eating, work up to this slowly both in terms of the duration of your fasts and how often you do them. It is also important to stay well-hydrated when fasting as the drop in insulin levels will trigger your kidneys to stop holding onto salt, which will take with it a significant amount of water. Excessive plain water drinking on a longer fast has the potential to lead to low sodium levels, so you might to add a pinch of salt or an electrolyte tablet that contains salt to some of your drinks over the fast.

Remember, humans have been practising fasting for religious reasons for thousands of years, and we evolved in an environment where access to food was often intermittent and unpredictable. Although our modern conditioning to eat regularly and snack often makes fasting feel ’extreme’, provided fasting is suitable for you (see above) it is a perfectly normal activity for your body. Most people’s bodies have significant fuel reserves in the form of fat, and the shift to ketosis will power your brain and body from those reserves very well. It is also worth noting that your feelings of hunger will not remain constant over the fast (tending to come in waves or at intervals) and will decrease or stop as your body enters ketosis.

A great source of information on time-restricted eating and fasting is Dr Jason Fung, and a couple of his books are listed in ‘Further Source of Information’ at the end.

What are the additional benefits of longer fasts?

  • Autophagy: Your cells identify damaged proteins and worn-out mitochondria (the power plants of your cells) and set them aside for breaking down into raw materials and the using to build new components or as an energy source. This process is called autophagy. In times of plenty (e.g. when eating regularly) your body is under less stress and turns down this process. However, when you fast, the body is stimulated to ramp up this process to generate an additional source of raw materials in the absence of normal nutrition. As we age, the natural rate of autophagy declines, and thus, the theory at least, is that kick-starting that process with time-restricted eating and (more likely) fasting will lead to mitochondrial renewal, waste removal, and immune system rejuvenation [7].

Why should you care about your gut microbiome?

The gut microbiome is a complex, thriving ecosystem of trillions of microorganisms living inside your digestive tract—primarily in your large intestine (colon). Think of it as a fully functioning organ made not of human cells, but of microscopic life that consists of bacteria, viruses, fungi, and archaea. In fact, you have more microbial genes in your body than human genes!

In recent times we have come to realise more and more that the gut microbiome has a number of important functions:

  • Digestion and fuel production: Your gut microbiome ferments complex carbohydrates, such as dietary fibre from plants (oats, beans, vegetables) that the human stomach and intestine cannot process. This fermentation process produces short chain fatty acids (SCFAs) which are the primary source of energy for the cells lining your gut. Feeding your gut cells leads to a healthy gut with a strong barrier. The SCFAs produced by your gut microbiome also enter your blood stream and provide an additional source of energy for your muscles [11].
  • Immune system optimisation: Your gut microbiome helps to ’train’ your immune system to differentiate between harmless proteins from food and good bacteria vs. pathogenic viruses and toxins. The assistance given to your immune system by a healthy, diverse, and well-fed gut microbiome helps to lower inflammation and reduce autoimmune response (such as ulcerative colitis and Crohn’s disease). In fact, evidence has emerged that not only does a healthy gut microbiome help to manage such conditions, but dysfunction of the gut microbiome actually has a causative role in them. [12]
  • The gut-brain axis: Your gut microbiome is in communication with your brain both via the vagus nerve and via chemical messengers. For example, a significant amount of serotonin (your brain’s ‘happy chemical’) and gamma-aminobutyric acid (your brain’s ‘calming chemical’) are produced by your gut microbiome. The health of your microbiome directly influences your mood, stress resilience, cognitive function, and even sleep quality.
  • Barrier defence & pathogen protection: When your gut microbiome is healthy, the beneficial bacteria take up more of the “real estate” and consume more of the available nutrients, leaving less room or food for harmful, invading pathogens to take root. This helps to prevent leaky gut syndrome (intestinal permeability) and protects you from toxic bacterial pieces slipping into your blood and causing systemic inflammation.

Further sources of information

The Examine website for independent, unsponsored meta-analyses of health research

The Obesity Code by Dr Jason Fung

The Complete Guide to Fasting by Dr Jason Fung

Food for Life by Dr Tim Spector

The ZOE web site, app, and gut testing

Metabolical by Dr. Robert Lustig

References

[1] Hall, K. D., et al. (2019).Ultra-processed diets cause excess calorie intake and weight gain: An inpatient randomized controlled trial of ad libitum food intake. Cell Metabolism

[2] Malik, V. S., Popkin, B. M., Bray, G. A., Després, J. P., Willett, W. C., & Hu, F. B. (2010). Sugar-sweetened beverages and risk of metabolic syndrome and type 2 diabetes: a meta-analysis. Diabetes Care

[3] Stanhope, K. L., et al. (2015). A dose-response study of consuming high-fructose corn syrup-sweetened beverages on lipid/lipoprotein risk factors for cardiovascular disease in young adults. The American Journal of Clinical Nutrition

[4] International Agency for Research on Cancer (IARC) / World Health Organization. (2018). Red Meat and Processed Meat: IARC Monographs on the Evaluation of Carcinogenic Risks to Humans (Volume 114). Lyon, France: International Agency for Research on Cancer

[5] Regmi, P., & Heilbronn, L. K. (2020). Time-restricted eating: Benefits, mechanisms, and challenges in humans. Nutrients, 12(6), 1778.

[6] Anton, S. D., et al. (2018). Flipping the metabolic switch: Understanding and applying the health benefits of fasting. Obesity, 26(2), 254-268.

[7] de Cabo, R., & Mattson, M. P. (2019). Effects of intermittent fasting on health, aging, and disease. New England Journal of Medicine, 381(26), 2541-2551.

[8] Cienfuegos, S., Gabel, K., Kalam, F., Ezpeleta, M., Wiseman, E., Pavlou, V., Lin, S., Oliveira, M. L., & Varady, K. A. (2020). Effects of 4- and 6-h time-restricted feeding on weight and cardiometabolic health: a 1-week randomized controlled trial in humans. Cell Metabolism

[9] Shibh, A., et al. (2023). Time-restricted eating w/o calorie counting vs daily calorie restriction for weight loss: a randomized controlled trial. Annals of Internal Medicine

[10] Liu, D., et al. (2022). Calorie restriction with or without time-restricted eating in weight loss. New England Journal of Medicine

[11] Valdes, A. M., et al. (2018).Role of the gut microbiota in nutrition and health. BMJ, 361, k2179.

[12] Ni, J., et al. (2017). Role of the microbiota in the pathogenesis of inflammatory bowel disease. Gastroenterology, 152(2), 361-378.