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Ketosis While Fasting - Biosense®
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Feeling (and getting) that keto high during your fast

You’re well into your fast and feeling great. You check your ketone levels, and realize that finally, you are in ketosis! Amazing! But – what does that all mean, and what are some of benefits of being in ketosis? Additionally, how did you get here in this fabulous place, and more importantly, how can you stay here?

To get ketosis, you’ll first have to understand your body a little better.

Getting in ketosis – and staying there

The human body is truly amazing. In fact, the reason you can stay alive in even the most extreme circumstance is because your body is built for the job and the job description hasn’t changed in millions of years. The body’s goal is to keep you in a state of normalcy (or, homeostasis) and really, it doesn’t care what you feed it as it will go on all measures to fuel on its terms. That preferred fuel is glucose. Why glucose? The body loves it because it’s easily converted in glycogen (the stored form) and is a ready source to keep you energized and alive. It’s also a fan because the brain loves glucose as well. So, imagine how the body feels when you take away its favorite fuel. It naturally revolts.

The first thing it will do is seek out any remaining droplet of glycogen left and try to get more. That means, if you’ve gone low carb but are still providing even small amounts detectable to the body, it will take it. You might be thinking about the obvious foods to forgo. A candy bar or a piece of bread. But the body will take any amount of carbohydrate, healthy or not – and run with it. But what if you’re not feeding your body any significant amount of carbs at all? When the body starts to sense it and it starts feeling desperate, it will then tap into the liver and ask assistance in forming new glucose from non-carbohydrate sources. From the body’s perspective, you are in an environment where food is scarce and it then goes into survival mode. If protein consumption is high enough, it will magically turn it into glucose. This process is called gluconeogenesis – or the new formation of glucose.

So here is how the scenario may play out. You started your keto plan on Monday, but for a year prior to that Monday you blew it out with carbs of all kinds, all day, every day. You’ve got a lot of fuel to get through. But you remained low carb since Monday, and by Thursday or Friday, you feel that you’ve really depleted these stores. The liver could step in there and start using byproducts of protein. But wait – the numbers on your monitor are still low. You moderate protein as well and start counting carbs so you can keep better track. A few days later, your body may have no choice than to look for alternative sources. That’s when the sweet spot hits – because there is only one source of fuel left – fat. While the body has entered an acceptance stage, the brain is not happy. That’s because the brain can’t fuel on fat. Therefore, it starts fueling on the byproduct of fat breakdown – ketones. This is when your numbers should start to reflect your efforts. It will vary based on where you started to begin with as well as your protein content.

You want to stay in ketosis while fasting – how do you eat to do that?

Achieving ketosis requires significantly reducing your carbohydrate consumption, which can be achieved through various forms of fasting. That doesn’t mean the diet is all bacon, all the time. Healthy fats such as avocado and olives can be central components of the diet in addition to non-starchy vegetables, nuts and seeds and sources of protein like fatty wild fish, eggs, and chicken. Coconut oil and full fat dairy such as hard cheese may also be included. Recent studies have also found that a more flexible approach (20-50g of carbohydrates) can still result in ketosis and weight loss, and may include more plant based fiber derived from previously eliminated nuts and non-starchy vegetables. This makes the diet less restrictive and more sustainable over time.

The long-term impact of a meat-heavy keto approach is unknown

There are numerous studies showing the positive impact of low carb diets, but few examine the long-term impact of a meat-heavy approach as seen in the ketogenic diet. Until more research is provided, there may some compelling reasons to rethink animals as the primary source of food. For starters, many of the meat prevalent in keto cookbooks include processed options like bacon and sausage. A recent study showed that even small amounts of red and processed meats may increase the risk for early death. Another reason to reconsider a meat-heavy keto approach is the impact it may have on the gut’s microbiome. While plants high in fiber, prebiotics, and probiotics can help good bacteria flourish, red meat, fried foods, and high fat dairy may quickly increase the bad bacteria in your gut.

Plant-based ketosis is possible

Plants are typically a source of nourishment on the ketogenic diet, but they often don’t comprise the fat portion. Instead, they act as the delivery system for vitamins, minerals, and fiber. Broccoli, spinach, kale, and cauliflower are all examples of nutrient dense, non- starchy vegetables that fit in well on the keto diet. However, finding plants that provide more protein and less carbohydrate are where the challenge begins. Seeds (such as hemp seed) and nuts (such as almonds) provide small amounts of protein but for more robust protein content, consider small amounts of soy in the form of organic, non-GMO tofu or tempeh to help boost protein. Further, if the plan is to only eliminate meat coming from four-legged animals, then eggs, fish and even dairy can be added into a vegetarian approach. Fats can be provided easily as well and may include nuts, (such as macadamia nuts), avocado, olives, coconuts and their oils, tahini, unsweetened nut butters, seeds (such as hemp, flax and chia) and flours (such as coconut or almond flours). A day on the plant-based ketogenic approach can vary but typically, its broken down into 5% allocated to carbohydrates, 30% allocated to protein and 65% or more allocated to fat.

Which “alternative” sugars can I have and still stay in ketosis?

More research is needed on the sugars that are popping up in keto-friendly products, but if you are using an alternative for baking or to simply put in your coffee, stevia, erythritol and allulose all appear to keep the body from releasing insulin or glucose.

You heard that keto can be “bad” for health. Is this true?

Any diet can be made unhealthy. The benefit or harm of the keto diet will depend on the dietary pattern chosen. Very low carbohydrate diets that lack sufficient vegetables and other important phytonutrients may harm health long term, but a keto plan that includes fiber rich plants, healthy fats, and moderate protein can be beneficial for weight management and reduce and manage chronic disease. Constipation may occur but may be avoided through the consumption of a higher fiber approach. Additionally, many individuals will experience what is commonly known as the “keto flu” which are unpleasant symptoms that can occur when the body is transitioning from a carb to fat burning mode. These symptoms are short term and subside as the body enters ketosis. Finally, as with any dietary approach, maintaining hydration is key to keeping your energy up and your bowel movements regular. Though the recommendation of eight, eight-ounce glasses of water every day is a good start, keep in mind that you may also drink decaffeinated coffee and tea for hydration. Your urine will be a good indicator of hydration status – look for a faint yellow color as a sign you’re well hydrated.

Ketosis can be a game changer for health

Multiple benefits have been associated with the ketogenic diet. The following are just a few benefits that may come with ketosis.

Weight Loss

A 2020 study conducted among obese adults 60-75 years of age found that a very low carbohydrate diet (VLCD) resulted in significant weight loss, especially visceral adipose tissue and intermuscular adipose tissue. The group, “experienced a 9.7% reduction in total fat mass” compared to a control group that had a typical low carbohydrate diet. The VLCD group had an average of 22.8% visceral adipose tissue decrease compared to the control with a 10% decrease. The study shows that very low carbohydrate intake can play a significant role in weight loss even compared to the typical low carbohydrate diet.

Metabolic Health

The weight loss study also showed an increase in HDL cholesterol with a very low carbohydrate diet that results in ketosis. The deemed ‘good’ cholesterol aids in removing other ‘bad’ cholesterol in the bloodstream that can cause heart disease.

A 2021 study comparing a low-fat diet with a ketogenic diet found that the keto participants had more stable blood sugar and insulin levels, despite eating more calories. This is critical, as recent data indicates that unstable blood glucose levels can increase appetite and lead to weight gain.

Another study published in 2020 assessing low carb diets in older individuals found improvements in body composition, fat distribution, and metabolic health. The diet may also play a role in the management of type 2 diabetes.


The ketogenic diet pushes your body into ketone metabolism which is a result from low carbohydrate supply. In a 2013 study, the ketone metabolism was compared to glucose metabolism to prove that ketone metabolism “produces fewer reactive oxygen species which are known to contribute to inflammation”.

Cognitive Health

Ketogenic diet has been used in children that don’t respond to drugs used to prevent epileptic seizures. To understand the science behind this diet, a 2005 study has shown that the effects keto has on the brain can lead to neuronal stability. This is because a calorie restrictive diet causes an “increase in the expression of genes encoding energy metabolic enzymes.”


Every individual’s cancer diagnosis is different. With that, most successful scientific studies have used mice and ketogenic diet and/or ketone supplementation to show its potential benefits. A 2014 study results show the trend of decreased tumor size and the spread of tumor among a group of mice supplemented with ketones. This shows hope that with further research the ketogenic diet used in supplementation with cancer treatments could be beneficial in tumor metastases.

Another animal study found that a ketogenic approach helped in survival and management of symptoms related to glioblastoma, a type of brain cancer found in humans.

Human Performance

The ketogenic diet has been difficult to study its efficacy with athletes and how they perform because of adherence to the diet and participation. However, in a 2019 study, compared to female athletes, male CrossFit-trained athletes showed a greater increase in fat utilization during a four-week ketogenic diet tested with submaximal intensity training. Drawing conclusions compared to a customary diet, the keto male athletes also had lower carbohydrate oxidation. This study shows that with further research and even increased length in diet adherence, the ketogenic diet can allow the body to break down fatty acids at a higher rate which may enhance athletic performance.

How do you know when your body is in ketosis?

You don’t know what you can’t measure. Increased ketone production is a sure sign of ketosis and can be monitored through the breath, blood, and urine but the accuracy of these methods, and the frequency of testing vary greatly. A recent clinical trial showed that a single daily ketone measurement is 50% less accurate than a time-weighted average, providing a poor reflection of actual ketone levels. Since ketones change quite a bit, much like blood sugar, it is important to check levels of ketosis as they are impacted by food and exercise, ideally 3-5 times per day. Urine strips are the least expensive but least accurate. For accuracy, and convenience, a clinically backed breath ketone device, such as Biosense is the best bet for tracking ketone trends in relation to diet.

Is the keto diet during fasting safe?

Studies show that low carbohydrate diets can be a safe and effective way for people diagnosed with type 2 diabetes or prediabetes for normalizing HbA1c levels, reducing the risk of hypoglycemia and assisting in weight loss. Ketogenic diets, however, are not for everyone and should be avoided by children and teens, type 1 diabetics, pregnant women, and individuals with disorders of the kidneys, gall bladder, pancreas, and liver. Talking with your physician first and working with a registered dietitian is recommended before starting on the ketogenic diet to reduce risks and improve short-term and long-term success for weight loss and overall health.

Getting to ketosis on a fasting plan (or during a dedicated ketogenic diet) is possible. Understand the variations in keeping you within a desirable range is essential to reaching your health and weight goals.

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