By Dr. Marvin Singh, MD
March 25, 2019

The big question on everyone’s mind, and one of the most hotly debated topics, is on what we should eat. What is seemingly an innocuous question seems to be the most controversial of them all. The reason why is because everyone is different. 

You can’t create a comprehensive diet program that will work for everyone. Many of the diet programs (let alone the research studies) that are out there don’t keep in mind that the gut microbiome is central to health (and disease). You lose site of the actual target when you don’t keep the global picture in mind and all you are focused on is one thing, like bloating or weight loss.

The things that all the good eating plans have in common are that they take out all the junk and try to put in more of the good stuff. By now, we should all know that processed foods, packaged foods, sugars, fast foods, junk foods, sugar sweetened beverages, and hydrogenated fats are bad for you. For many, just stopping the intake of these unhealthy foods can make a big difference. That may only get you so far, however. The reason is because we need to understand how food works and what it can do for us. Food really is medicine!

I don’t like the word “diet” because it implies that you start something for a purpose and then you will probably be done at some point. That’s not how life and health works. Real diets for your longevity are more like lifestyle plans; they stay with you for life. So, how do you figure out a plan that will be able to stay with you for life? Let me break it down for you a bit further.

The Keto.Fast.Flex plan is one that can appeal and accommodate anyone. Before you start getting out the pitch forks, thinking that I’m advocating a high meat diet, you should know that a vegan can be keto also. So, hang on for a minute

The ketogenic diet has been around for a long time. It is a high fat, low carbohydrate diet and it has been used for almost 100 years in the treatment of epilepsy. There is also some more recent data regarding autism, chronic pain, and even cancer ( It’s not for everyone, though. It has a purpose. Just think of it like this: our body has two main sources of fuel—sugar and ketones. Sugars come from carbs and ketones come from fats. Our default mode is to run on sugars but our brains and our whole body actually runs quite nicely on ketones as well. When you restrict carbohydrates you are running off the fat and revving up your body to burn more fat. Thus, the whole “fat for fuel” phrase that everyone has been chanting these days. (Side note: you have to make sure the quality of the food is high because all fat is not created equally; also, you are allowed to eat vegetables!). You should know that the ketogenic diet, in the short term, can actually decrease the diversity of the gut microbiome but this improves after about 6 months in one study on patients with multiple sclerosis ( So, this may not be something to keep doing forever in all situations. In certain settings like neurologic conditions, cognitive disorders, seizure disorders, obesity, and metabolic syndrome, the ketogenic diet makes sense, at least for a period of time. Think of it as a turbo booster, a jump starter. There are certain situations where you shouldn’t really be doing a ketogenic style diet (eg, children without epilepsy, severe weight loss, eating disorders, pregnancy, metabolic disorders) and this is why it is important to talk to your doctor before making any big changes in your lifestyle and have them monitor you while you are on this diet as well. Even if this is the case, you can still follow this plan…just say “hello and goodbye” to the Keto phase and move straight to the Fast and Flex phases!

There is also a lot of data out there about intermittent fasting and its benefits. When we fast we convert the white fat cells (which store all the calories) to the beige fat cells (which burn energy). One recent study showed that every other day fasting can selectively activate beige fat, likely by impacts on the gut microbiome, and this could help control metabolic syndrome and obesity ( Cycles of the fasting mimicking diet can reduce intestinal inflammation, increase stem cell numbers, stimulate protective gut microbes, and reverse intestinal pathology when there is a chemically induced colitis (

It’s nothing new that a ketogenic diet can help you grab the bull by the horns and regain control over your metabolism and weight. In some cases, it may be just fine to continue it for the long run. However, in many other cases, it may not be possible, necessary, or safe. Nonetheless, the first stop at trying to regain control over your health and weight loss could be found in the ketogenic diet, which is Phase 1 of the Keto.Fast.Flex Plan. As I was developing this plan, I found that for me, I found benefit in doing Keto for about 3 months and after the first month, when things seem to be settled, I introduced fasting. I started with a basic fast and then tighten up the eating window. Then periodically I would practice fasting mimicking style eating. If anyone has a desire, need, or indication to cycle off the ketogenic style of eating, I still continue to suggest including fasting. But, then what next?

Well, that’s the fun part. If you want to be able to maintain health and wellness while keeping the gut microbiome and whole health in mind, you have to acknowledge that it is YOU that is following this plan, not the masses. If you have Hashimoto’s Thyroiditis, Crohn’s Disease, Ulcerative Colitis, Bloating, SIBO, Obesity, Fatty Liver, Diabetes, or Heart Disease, there is going to need to be some sort of adjustment. Also, and most importantly, you have to allow for flexibility. Don’t tell me you’re never going on a vacation or doing anything fun with friends because you have to stay on your restrictive diet. We weren’t designed like that. Humans are social animals. Go out there, have fun! Live your life! If you like the Keto-Fast part and that’s what resonates with you and you have been able to work with someone to tweak particulars of it that fit you best, then that’s great. If you break out of ketosis for a while when you are on vacation or chaperoning your kid’s field trip, who cares! Don’t beat yourself up over it. But, when all the fun is done, you’re probably going to have to give yourself a turbo charge boost again and re-induce the ketogenic stage and even consider a little more regimented fasting plan after things settle…then you can find your way back to Flexing again. Maybe you also realize that ketogenic diet is not for you…it was nice when you were doing it and you lost some weight, but it’s not practical for you. That may be because, for many it really is not a practical long term plan (and/or there are other factors that need to be optimized as well). It’s ok to Flex to a method of eating that doesn’t keep you in ketosis, but that also doesn’t mean the first stop is the drive through window either! It helps to look at what’s going on in your gut microbiome, life, health, genes, and many other things in order to best optimize the Flex aspect for the long run. I personally like cycling out of ketosis and following a lower carb, balanced eating plan. It gives me the chance to diversity my diet, eat what’s in season, and expose my microbes to different things while building resiliency. After a few months of Flexing, I’m right back to Keto and Fast.

If I can do it, you can do it too! Remember, we weren’t built to live regimented strict lives where we can only eat one way, or the way a study was designed for people that have nothing in common with you. Eating clean, whole foods in a ketogenic style can get your metabolism revved up and ready to burn fat. Fasting can help you reset by allowing your body to rest. And allowing yourself to Flex acknowledges that life happens, things change, and that you are unique and should be doing what’s best for you so you can live longer, healthier, and happier!