By Mukaila Kareem
As a major product of photosynthesis, glucose is one of the most abundant biomolecules on the planet earth. All living cells can use glucose and arguably the prevalence of modern chronic diseases is largely dependent on amount of glucose ingested over a long period of time. For whole-body survival, taking up glucose from of blood by different organs and systems is non-competitive under normal condition. For example, the brain, red blood cells, smooth muscle of blood vessels, the lens of the eyes, the nerves in the body, some part of retina and kidney have high affinity for glucose. These organs and tissues can maximally take up glucose at low or high blood concentrations without the need for insulin. To prevent excessively low blood concentration or diabetic shock, large metabolic organs such as the skeletal muscles, liver and fatty tissue have low affinity for glucose and prefer fatty acid substrates at rest and during fasting but would readily switch to glucose as the main source of energy during feeding when the concentration of blood glucose is remarkably high. These helps to bring the blood sugar concentration back to normal level. However, to “fund” the expensive picky brain’s love for glucose, the liver is able to store up to about 100 grams of glucose, worth at least 7,000 calories in form of glycogen otherwise called “tissue starch”.
While the red blood cells and retina are exclusively glucose dependent, the expensive and selfish brain is however not suicidal and would entertain other substrates under short term conditions. For instance, under life threatening events often called fight or flight, the brain can switch from glucose to lactate substrate, an intermediate energy source spurns off by the working skeletal muscles, while fighting or fleeing under what is called anerobic respiration. However, in fasting state, when the liver exhausts the stored glycogen worth about 700-900 calories in say 10-12 hours, the brain can also switch its energy preference from glucose to ketones, a fat derived energy substance. This leads me to the ongoing popularity of “nutritional” ketogenic diets even in tropical countries, such as Nigeria, where the staple foods are mostly carbohydrates.
I am not against dietary fats and I think we are reaping the whirlwinds of modern chronic diseases largely due to demonization of saturated fats in the last 60 years. In fact, keto diets are great options for weight control and diabetic reversal for those who can afford it. In due course I would do a series of writings on dietary fats and ketogenic diets, but the fact remains that not everyone in developing countries who are struggling with weight and other health issues can regularly afford expensive steak, bacon, organ meat, salmon, tuna, eggs, butter and cream, almonds, avocado, and cheese.
For sure, our human ancestors did not hit ketosis by constantly consuming dietary fats. They had no food pantries and no refrigerators full of ready to eat meals and had to be physically fit for the daily hunting and gathering to kill wild animals on rare occasions. For the most part, they were failed hunters and largely lived on wild fruits and tubers (high carb) which obviously were plant products that could not run for dear life like wild animals. Humans have not always lived on 3 regularly spaced meals and snacks, so the popular phrase about “a(n) hungry man is an angry man” is purely based on occasional failed expectation of food regularity. During my University days in the 80s, a lot of us lived on no breakfast, lunch and dinner and sometimes no breakfast, no lunch and dinner in what we popularly called zero-one-one or zero-zero-one and I do not recall anyone getting angry walking to the lecture halls in fasting state. Like our ancestors, modern day hunters and gatherers still forage in fasting state and anyone who has experienced “post lunch slump” would know it is not a good idea running after some wild games on full stomach. We have more than enough energy sources stored within the body before the next meal.
In fact, we are bundles of energy depot on two legs: According to a renowned endocrinologist, Dr. Michael Jensen, one kilogram of fatty tissue stores about 7,000 calories which is enough to provide all energy needs of an average woman for a whole 3 days. According to him, a normal weight 60kg woman with 30% body fat (18kg) has 2 months of energy stored in fatty tissue. The reality is that the body would never have access to these stored fats without intermittently depleting about 100 grams of glycogen stored in the liver either by fasting and/or physical activity or by any prevailing fad diet. Once the liver glycogen is exhausted, the body would mobilize these stored fats by breaking them to fatty acids and glycerol. However, the brain cannot use fatty acids directly as they do not cross the blood brain barrier, but the liver helps to “pre-digest” the fatty acids to ketones which have no problem crossing the brain barriers as energy substitute for glucose.
If dieting works long term, there would be no multibillion-dollar weight loss industries and this article would not be necessary either. Not just keto diets, several studies have demonstrated compliance failure as far as dieting goes in general because people find it hard to stick with any kind of diet if left on their own devices. As noted by two nutrition experts in an article titled, we need hope not hype: “… no diet has yet been shown to be uniformly easier to stick with than another in the long run.” It should be pointed that fasting is no dieting and important to be reminded that a healthy person stores an equivalent of 2 months’ worth of groceries as fats. There are 24 hours in a day, fasting occasionally 12-16 hours few days a week costs zero amount to access “these giant fat groceries” within our bodies and still able hit ketosis without sacrificing our favorite foods on non-fasting days. This is especially important for an average person in developing countries who can not afford the expensive high fat low carb diets. The goal is to hit ketosis, few days of fasting in a week is as good as expensive keto diets on your favorite meals. This has always been the only way human have survived for centuries under food uncertainty.
Kareem is a Nigerian trained physiotherapist who resides in the USA, and his expertise is on physical activity and health.