Ketosis is a bio-chemical process that occurs naturally, and it means that the body converts fat into usable energy for itself. Energy is needed for everything the body does. Fat is converted to energy and the chemical by-product of this process is called ketone bodies, hence the name ketosis. It should not be confused with diabetic ketoacidocis which involves very high levels of ketones and is possibly fatal.
Ketosis usually occurs when there is a lack of glucose, or carbohydrates (carbs), needed for performing tasks the body needs energy for, such as exercising to a sufficient degree for a sufficient period of time (whatever that may be), or by fasting. As many have heard, it is also normally possible to induce this metabolic state by sticking to a low-carb, and possibly high-fat, diet. More on my personal experience with that below.
The general reasoning seems to be that once you deprive the body of carbohydrates to a sufficient degree, by following a strict diet, it will start to deplete the body's fat reserves in order to produce energy. The body switches from a state where it burns carbohydrates for energy, into burning fat. This releases ketone bodies, also called ketones, into the blood, and the elevated levels can be measured.
There has been considerable focus on ketosis in recent years, particularly with regards to dieting, health concerns and potential weight/fat loss. As with any - or most - topics, you will find people with completely opposite opinions, even if they are presented with the same information.
Find out how many carbs, how much fat, how much protein and much more about more than 1100 food items by visiting www.howmanycarbs.org.
In my personal experience, inducing ketosis through a low-carb diet works as a tool for losing weight. I did not notice anything feeling horribly wrong with my body, but there was certainly a noticeable change and some fatigue. It's difficult to pin-point exactly what it felt like. Studies conducted in recent years seem to indicate it is safe for most people (see Reuter's link below), but the topic remains controversial. I have read that common "beginner mistakes" are "not enough water and not enough fat", but personally I was concerned with the, for decades, traditionally touted heart/cardiovascular ill-effects from an excessive saturated fat intake. I was worried even after reading seemingly credible material indicating that a low-carb/high-fat diet only temporarily (for about 6 months) increases cholesterol and other "bad" levels. Read more about the study on Reuter's site. In fact, the low-carb/high-fat diet had a slight advantage on a low-fat diet according to that study. Then again there are different types of fat. I personally decided not to increase the fat intake deliberately, but just ate low-carb stuff where some of it contained fat and some didn't. Sadly, I don't have exact numbers. Do as you feel is right. In my experience, your body often lets you know when you need to change something (like coughing from cigarettes, to mention one extreme).
According to the above referenced Reuter's article, the weight loss itself is similar with both a low-carb/high-fat diet and a low-fat/low-calorie diet. My gut feeling is that the low-fat variant will be healthier for people whose bodies can not cope with high cholesterol levels or other detrimental effects from a high fat consumption. Typically cardio-vascular or heart disease would be factors to consider.
I would recommend taking great care before starting on a high-fat diet. Also, in retrospect, I realize that I was probably malnourished somehow. I simply did not eat enough, and with neither enough carbs nor fat, or other nutrients, there was fatigue and hunger. Typically, people say they do not feel hungry on a low-carb diet, but I didn't "do it right", so I was very hungry most of the time. Alcohol seemed to kick in more than usual as well, along with its negative effects. After I ended the diet, I felt a strong need for eating very regularly.
You can get products usually bearing names like "Ketostix", "Ketosticks", or similar, which you urinate on, and subsequently observe a color change on, if you have entered ketosis. I found that I would apparently go in and out of ketosis apparently for no reason. Twice I linked going out of ketosis with diet soda intake. The artificial sweetener used in said products was aspartam. I can definitely not verify that for sure, but it struck me both times, as I hadn't eaten anything with carbs, but had just had fairly large amounts of diet soda. Coffee seemed to be OK, but I cannot verify that definitively either. Most resources I have read say coffee will not affect the ketosis state. There might be individual variations.
I was told by a friend about the concept of a low-carb diet, and after she had lost 24 kg / 53 lbs (pounds), I decided to try for myself, while panicking a bit after I suddenly gained 7 kg / 15 lbs, without really knowing why, and already being about 25 kg / 55 lbs overweight in my opinion.
Some background info: I was very skinny in my early 20s. That picture to the left indeed is of me, and was taken when I was 19 or 20, I think. At the lowest I weighed only 55 kg / 121 lbs, after I had been losing weight for a few years due to lack of exercise (those were the days...). I started losing weight after I left the service in the armed forces, where I was at the more ideal weight of 65-70 kg / 143-154 lbs. I'm 170 cm / 5'7" tall. After I started taking a certain type of medication (neuroleptica), I basically gained 30 kg / 66 lbs in about 6 months, without altering my eating habits at all, to my knowledge or recollection (it's been over a decade). Gaining weight is a known side-effect of the medication. If only I had objected. Oh, well; older and wiser; onwards and forwards, etc.
I was at 102 kg / 225 lbs when I started on the low-carb diet. I spent time reading how many carbs various foods contained and made sure I didn't eat more than 15-20 grams / 0.7 oz of carbs per day. I also had no alcohol what so ever for the first three weeks (not always too happy about that). Basically I followed the Atkins-recommended way, except I didn't increase fat intake. I carried on with this for three weeks, and I had lost about 5-6 kg / 11-12 lbs. The weight would vary and go up and down by about 1-2 kg / 2-4 lbs, but in the end it went down more than up. After five weeks I had lost 10 kg / 22 lbs. That's an average of 2 kg / 4.4 lbs per week.
Then came creeping a lack of motivation and gradually I returned to a more normal, medium-carb diet. I considered the diet temporarily over after about 4 months and started "misbehaving" quite a bit after about two and a half months, so the weight loss was slowed to a crawl. All in all, I lost 15 kg / 33 lbs and am now at 87 kg / 192 lbs. I hope to find the motivation and drive to try again and hopefully shed some more fat soon.
Somehow the ketosis process affected my breath and gave me a pretty "bad taste" in my mouth, which is said to be due to the ketone bodies that are released - although most of them are released through the urine, which will probably also smell differently. People seem to compare the smell to acetone, which you'll find in products like nail polish.
Apologies to the faint of heart, but I feel I have to mention this: The friend who told me about the low-carb concept said it cured her stomach problems. For me it was different than before, but still a problem. I would brutally eject some fluid shortly after having woken up from a longer sleep, every time. I basically got no fibers, so that's my guess as to why it was always just that fluid and no "texture" (don't worry, I didn't, and don't, touch it).
Note: This is not "The Absolute And Unquestionable Truth" on the topic, but the writing herein is parts of obtained (presumable) knowledge, and I also draw on concrete personal experience. Hey, even the laws of physics have changed (or have at least been refined) on occasion, so a little disclaimer might be wise. What I present as facts, such as what ketosis is, should be well-established facts by now, though, and I have researched the topic.
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Author: Joakim Svendsen.