Great question. So if you are already in nutritional ketosis from your diet, exogenous ketones would still help raise ketone (energy) levels when you want that (maybe for focus at work or energy at the gym. They also help get you back into ketosis after cheat meals and skip the “keto flu” which is the period when your body is using up stored glycogen.
The body will start making ketones when either we go extended periods without food, or we restrict the one dietary component that stops ketone formation – this being carbohydrates and also minimising protein intake as this also can halt ketone. In turn, your primary source of food is fat, with very little carbohydrate and a small amount of protein.”
Until there is more definitive information on the necessary blood levels and the differing proportions of BOHB an AcAc to optimize cellular and organ functions, it will be difficult to specify the dosing and duration of supplemental ketones. However for fuel use, and very likely for exercise performance as well, sustained blood levels of BOHB in the range of 0.5 mM to 1.0 mM are likely to be required. This is achieved physiologically by an estimated ketone production of 50-100 grams per day in a keto-adapted human.
Ketostix are very unreliable. There are many factors which can alter results such as hydration level, if you’ve worked out recently and the amount of unused ketones in your body to name just a few. Never rely of Ketostix to determine whether you are in ketosis or not. The Precision Xtra blood ketone monitor is the gold standard for testing for ketones in your body. After following a ketogenic diet for a while, you should be able to tell if you are in ketosis or not by the way you feel.
 “Though the small amount of carbohydrates in the diets may be more than balanced by the potential sugar production from the large amount of protein to keep the ratio of fatty acid to glucose below the generally accepted level of ketogenesis, the respiratory quotient data suggest another mechanism also” ß (most likely the CPT-1A mutation, which had not been discovered at that time)
Importantly, at Diet Doctor we do not think you need to spend any extra money at all in order to revolutionize your health. You can achieve radiant health just by enjoying authentic food that is naturally low in carbohydrates, getting plenty of sleep and some exercise (going for a walk is free) and reducing stress. A lot of you who answered the survey made exactly these points in your explanations of reasons for not taking the supplements. I whole-heartedly agree.
Intermittent fasting is using the same reasoning – instead of using the fats we are eating to gain energy, we are using our stored fat. That being said, you might think it’s great – you can just fast and lose more weight. You have to take into account that later on, you will need to eat extra fat in order to hit your daily macros (the most important thing). If you’re overeating on fats here, you will store the excess.
When you are in a state of ketosis, the body turns fatty acids into ketones - these appear as beta-hydroxybutyrate in the blood. Measuring blood ketones is regarded as the gold standard and most accurate way to track ketone levels. Testing this way can be expensive, its can cost up to $3 a strip, so if you're testing multiple times a day it can get pricey.
Let me introduce myself. My name is Mark Sisson. I’m 63 years young. I live and work in Malibu, California. In a past life I was a professional marathoner and triathlete. Now my life goal is to help 100 million people get healthy. I started this blog in 2006 to empower people to take full responsibility for their own health and enjoyment of life by investigating, discussing, and critically rethinking everything we’ve assumed to be true about health and wellness...
We are told by our parents, doctors, and the media that milk builds strong bones and that we should take calcium supplements to help protect against osteoporosis. Indeed, calcium deficiency can lead to a plethora of health problems[12]. However, those of us who take calcium supplements or consume calcium-fortified foods and beverages may, in fact, be consuming above the Recommended Dietary Allowance (RDA) of calcium.

Animal research findings report that BHB supplementation also enhances oxygen utilization, especially in the central nervous system (CNS).[11] While molecular oxygen is a crucial molecule for health and longevity, too much of it can be potentially toxic and speed the effects of aging in tissues throughout the body.Therefore, using a BHB supplement can effectively mitigate the toxic buildup of molecular oxygen, particularly in the CNS/brain.
More tolerable than MCT oil: MCT oil has been known to cause gastrointestinal distress in users, especially when taken in higher amounts. Exogenous ketones in the form of ketone salts, in comparison, are well-tolerated. Thus they enable one to avoid adverse GI events while providing the body with similar types of benefits. Figure 2 shows Ketone esters can be effective at reducing appetite. A combination of MCT oil and exogenous ketones may aid weight loss and allow a lower loading of ketone supplements, without the GI distress seen with MCT oil.

Other ingredients: Many of the supplements contain large amounts of caffeine – the supplement we tested from Prüvit contains the same amount as a 16 oz cup of coffee! Some supplements also contain malic acid, which is “known for its ability to increase energy and tolerance to exercise”. This leaves the nagging doubt: if the experiment shows an increase in energy and physical performance, for example, how do we know it is the (expensive) BHB causing the effect and not the (inexpensive) other ingredients?

Because of how effectively exogenous ketones can reduce hunger for those in ketosis, pay attention to the cues your body gives you. It’s possible to extend your fasts longer than necessary because of a decreased appetite cue. While those who have some weight to lose might be tempted to think this is a favorable side effect, there is a difference between fasting and starving for nutrients. Make sure to get enough food to support your activities and maintain your muscle mass.

Pruvit v Perfect Keto: One of the more popular brands for BHB salts is Pruvit (Keto OS). Pruvit is a good brand, but they do use some additives. Also, Pruvit is an MLM company that has tons of people pushing their products as the best weight loss product in the world. And you have to use one of their representatives’ referral codes to buy it. Learn more about the two in this Pruvit vs Perfect Keto comparison article.

If you are not on a vigorous exercise plan, I wouldn't go more than about a scoop a day (if you are a 30min/day, low carb person like me) because some of the research available says that if you get into ketosis using diet only and supplement with extra ketones, you may experience a slower rate of weight loss since you are getting your ketones from a supplement rather than the body transforming fat to ketones. As I progress, I will probably move up to 2 scoops per day.

Glucose and BHB went down slightly throughout the effort and RQ fell, implying a high rate of fat oxidation. We can calculate fat oxidation from these data. Energy expenditure (EE), in kcal/min, can be derived from the VO2 and VCO2 data and the Weir equation. For this effort, EE was 14.66 kcal/min; RQ gives us a good representation of how much of the energy used during the exercise bout was derived from FFA vs. glucose—in this case about 87% FFA and 13% glucose. So fat oxidation was approximately 12.7 kcal/min or 1.41 g/min. It’s worth pointing out that “traditional” sports physiology preaches that fat oxidation peaks in a well-trained athlete at about 1 g/min. Clearly this is context limited (i.e., only true, if true at all, in athletes on high carb diets with high RQ). I’ve done several tests on myself to see how high I could push fat oxidation rate. So far my max is about 1.6 g/min. This suggests to me that very elite athletes (which I am not) who are highly fat adapted could approach 2 g/min of fat oxidation. Jeff Volek has done testing on elites and by personal communication he has recorded levels at 1.81 g/min. A very close friend of mine is contemplating a run at the 24 hour world record (cycling). I think it’s likely we’ll be able to get him to 2 g/min of fat oxidation on the correct diet.

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