Be in ketosis!
Allulose StoreHow to determine ketosis with a continuous glucose monitor (CGM) without blood tests
The essence of nutritional ketosis is simple: when the body does not get enough glucose, the liver produces ketone bodies, mainly beta-hydroxybutyrate (BHB), from fatty acids.
The question is not how it works, but how to know if this state is already/still in effect.
Accurate measurement and its practical limitations
Even today, the precise determination of ketone levels is only possible from capillary blood.
Zones used in clinical practice:
• 0.0 – 0.5 mmol/L: baseline ketone level, no ketosis
• 0.5 – 1.5 mmol/L: slow fat burning, the start of nutritional ketosis
• 1.5 – 3.0 mmol/L: moderate, optimal fat burning
• 3.0 – 5.0 mmol/L: rapid fat burning
• Above 5.0 mmol/L: starvation ketosis, above 10 mmol/L risk of ketoacidosis
Measuring blood BHB is accurate but cumbersome. It requires a finger prick, test strips, and multiple daily measurements, which is why few people do it regularly in everyday life.
Urine acetone strips indicate with a 12–24 hour delay, and breath acetone measurement shows individual variation.
In contrast, a continuous glucose monitor (CGM) is now widely available, provides minute-by-minute data, and is non-invasive.
Two related curves
The physiology of water fasting provides a well-reproducible pattern.
The first correlation is the rise in ketone levels over time:
• 24-hour fast: ∼1.0 mmol/L – fat burning has started
• 36-hour fast: ∼2.0 mmol/L – optimal fat burning
• 48-hour fast: ∼3.0 mmol/L – rapid fat burning
The second correlation is the mirror movement of blood glucose and ketones over 72 hours. As blood glucose decreases, ketones increase, as the same hormonal environment – low insulin, elevated glucagon – regulates both.
Measured blood glucose and ketone average values during water fasting
It is this inverse proportionality that makes estimation possible.
How can ketosis be estimated from CGM data?
The table does not claim that glucose equals ketones. It shows which glucose pattern is associated with which ketone zone.
The estimation is based on three parameters:
1. Average fasting glucose
If the fasting average is between 4.0–5.5 mmol/L for 3 consecutive days and there is no post-meal spike above 5.5 mmol/L, this most likely corresponds to an optimal ketone zone of 1.5–3.0 mmol/L.
2. Glucose variability
In ketosis, daily variability is low. A CV (coefficient of variation) below 15% and nocturnal fluctuations below 0.3 mmol/L indicate the beginning of nutritional ketosis.
3. The 24–48 hour rule
If the average drops below 4.5 mmol/L after 24 hours, fat burning has started. If it is stable below 4.2 mmol/L after 36 hours, we can speak of an optimal zone; if it remains below 3.9 mmol/L after 48 hours without symptoms, we can speak of rapid fat burning.
In practice, therefore, laboratory-grade precision is not needed, but rather zone classification. To answer the question of whether the body is in ketosis, a combined assessment of the CGM trend and the above table is sufficient.
When is this estimation not applicable?
The glucose-ketone relationship cannot be evaluated in the case of type 1 diabetes, SGLT2 inhibitor treatment, pregnancy, or extreme protein intake (>2.5 g/kg of body weight). In such cases, only blood BHB measurement is authoritative.
Summary
An exact ketone level can only be determined from blood, but the existence of ketosis can be estimated from continuous glucose monitor data if the 72-hour inverse dynamics of blood sugar and ketones are known.
Glucose levels corresponding to values of 1.0 mmol/L at 24 hours, 2.0 mmol/L at 36 hours, and 3.0 mmol/L at 48 hours provide a guide as to whether the body is in the baseline, slow, optimal, or rapid fat-burning zone.
Staying in ketosis is greatly facilitated by using Allulose Sweetener.
May the Sky, and ketosis, be with you! 🙂
This text is for educational purposes and does not constitute medical advice. Consultation is recommended before starting longer fasts or dietary changes.
