At the risk of repeating myself, I must stress again that the therapeutic benefits of a ketogenic diet come from the production of ketones, which requires insulin levels to be sufficiently low. Insulin levels are low when carbohydrate intake is minimized.
So the big question is — how low is low enough? The answer is — it depends.
FINDING YOUR LOWER LIMIT
Ketones are produced at up to 100 grams of carbs per day, but levels over 70 grams are typically reserved for the very insulin sensitive and elite athletes.
Most people will produce ketones when consuming about 50 grams of carbs per day. At that level, research shows it typically takes about three days to enter ketosis[1]. But if you’re overweight, insulin resistant, or suffer from a metabolic disorder, that number is likely to be much lower.
To guarantee ketosis, a daily carb limit of 20 grams is recommended[2]. But most of the population (like 99%) will produce ketones when consuming about 30 grams of carbs per day. So that’s where I started.
SO WHY IS THIS WEBSITE CALLED 25 CARBS?
I’ve assumed a 5 gram/day error rate in my measurement system, for the following reasons:
- I’m human, and sometimes make errors in tracking my macros.
- Most food tracking apps are open source, and are therefore prone to errors and inaccuracies.
- Manufacturers round-off nutritional information according to serving size. This is especially problematic for dairy products.
- Nutrition labels are often inaccurate, especially since US/Canada have different labeling guidelines than the rest of the world.
- Macronutrients for whole foods (meat, fruits, vegetables) represent a “typical” sample, and can vary greatly by cut, variety, ripeness or preparation.
Therefore, I target 25 grams of carbs per day to make sure I stay below 30 grams.
HOW DO I KNOW MY LIMIT?
There are three ways to know if your carb limit is low enough to produce ketones:
- Use a blood ketone meter
- Use urine ketone strips
- Cut your carbs to the bare minimum, and don’t deviate.
Option 1: Blood ketone monitors
The only way to know with 100% certainty your body is producing ketones is to use a blood ketone meter, similar to the blood sugar meter used by diabetics. These are now readily available and not terribly expensive (typically less than $100), but be sure to factor in the cost of the test strips.
Ketone meters measure the level of beta-hydroxybutyrate (BHB) in the blood. BHBs are the key compound in ketone molecules.
You need to see a reading of at least 0.5 nM (nanomols per litre), but you should target at least 1.5 nM. Note that ketone levels vary throughout the day. Sleep, stress and hormone levels (particularly for women) will also affect your results.
For anyone interested in purchasing a ketone meter, Diet Doctor reviewed four of the most common monitors. Be sure to be consistent about your testing technique, and don’t get too distressed over individual test samples. The general average is more important.
I recommend blood ketone monitors for anyone that does a “soft” keto diet, and doesn’t want to track macros.
Options 2: Urine ketone strips
When I started this diet in 2015, blood ketone monitors were hard to find. The most common testing method was urine ketone strips or sticks.
Keto sticks measure acetoacetate content, another key component of the ketone molecule. These test strips are relatively inexpensive, and were traditionally used to prevent ketoacidosis among diabetics.
The sticks typically start out beige, and transition to a deeper shade of pink or purple, depending on the amount of ketones in your urine. They’re not terribly accurate, but do provide a quick and dirty estimate for anyone just starting out.
Once you become fully keto-adapted, your body becomes more efficient at producing and consuming ketones, so there may not be excess ketones flushed away in your urine. The sticks therefore lose their effectiveness over time.
My sticks never turned purple, even at the beginning. I was always in the pink zone, probably because I try to stay well hydrated (water intake will obviously reduce the concentration of ketones). My sticks no longer change colour, so I’ve stopped using them. But I did find them reassuring at the beginning, when I wasn’t sure if I was actually in ketosis.
Once again, try to be consistent in your testing. Try to test at the same time every day, and don’t get too discouraged if your strips never turn bright pink or purple. Mine certainly never did.
Option 3: Be strict about your carb limit, and have faith in the process
The third option is what my brother calls “hard” keto.
Basically, pick an upper carb limit that will virtually guarantee ketosis, like 25 grams per day, and stick to it, come hell or high water. Unless you are a genetic anomaly, you will eventually enter ketosis, likely in just a few days.
MY RECOMMENDATION
The route I chose was option 3, “hard” keto. I used the keto sticks at the beginning, but they weren’t necessary. In hindsight, I was just being paranoid.
If you’re doing a dramatic change in carbohydrate intake, be ready for a shock. Since sugar is addictive, your body will go through sugar-withdrawal, leaving you feeling completely drained, lethargic and highly irritable. Before doing a major change, it’s a good idea to know your starting point.
I tried the Atkins diet back in 1999, dropping my daily carb intake from about 300 grams to 30 grams. I felt absolutely horrible, and gave up after only a few weeks. There were a lot of mistakes made in hindsight, but you should be prepared for severe sugar-detox if you’re transitioning into keto from a high-carb diet[3].
After my failed Atkins experiment, I switched to a more “balanced” diet, eating about 200 grams of carbs per day. Pre-keto (mid-2015), I was doing about 100 grams per day, down to 50 grams by the fall, down to 25 grams by December. My sugar withdrawal symptoms were minimal.
I’m a big advocate of a slow transition. Start by eliminating pure-sugar foods and drinks (soda, candy, ice-cream and slushies), then gluten (bread and pasta). Move on to pure-carb foods (cereal, rice, potatoes), then pair down on desserts and sweet treats. Then work on reducing your fruit intake.
Spend a few weeks on each step. Carefully measure your progress. Look for lower-carb options of your favourite foods. Slow and steady wins the race, most of the time[4].
Once you’ve picked a maximum daily carb limit, the next step is to figure out how much protein you need.
NOTES:
1 Note that production of ketones and becoming keto-adapted are not synonymous. While ketone production can begin within a few days of starting a low-carb diet (or fasting), keto-adaptation can take several weeks, or even months.
2 I have read a few cases of people who say they have zero carb tolerance, but this is usually in reference to those suffering from serious chronic diseases, typically arthritis or MS, or often just used as an excuse to not eat vegetables.
3 If the smell of freshly baked bread or cookies gives you a happy, warm feeling, you’re not alone. High-carb foods release dopamine, the neurotransmitter responsible for pleasure, and the same chemical responsible for crack addiction. The more sugar you eat, the more sugar you need to get “high”. Conversely, sticking to a low-sugar diet will reduce your cravings for high-carb foods.
4 Most keto-evangelists would disagree with this statement, and instead tend to advocate cutting carbs cold turkey. Although this didn’t work for me, it might be an option worth considering.