Although my initial plan was to include this post in All You Need to Know About Carbs on Low-Carb Ketogenic Diet, I decided it deserves to be discussed separately.
How Many Carbs per day to stay in ketosis?
As described in my post How Does the Ketogenic Diet Work? Weight Loss and 3 Main Effects of Ketosis, weight loss on a ketogenic diet is achieved by limiting the daily intake of net carbs and getting your body in a metabolic state known as ketosis.
While in ketosis, your body effectively uses fat for fuel. In general, the daily intake of net carbs required to enter ketosis could vary from 20 to 100 grams per day (and very rarely over 100 grams per day). Most people, who have experienced ketosis, claim to have reached that state at about 20-50 grams of net carbs per day. I'd suggest you start at 20-30 grams and see how you can adjust it for your needs.
There are two ways to find your ideal net carbs intake:
Low to high method
Start from a low level of net carbs to ensure you quickly enter ketosis (~ 20 grams of net carbs per day). When you detect ketosis after about 2-3 days, start adding net carbs (about 5 grams each week) until you detect a very low-level or no ketones (using Ketostix or blood ketone meter). This is usually the most reliable and quickest way to discover your net carbs limit. It could be a bit hard the first couple of days, as you have to give up almost all carbs from one day to another but it will be worth it. This method is highly recommended.
High to low method
Assuming you're not in ketosis, start from a relatively high level of net carbs (~ 50 grams) and keep reducing (about 5 grams each week) until you detect presence of ketones. This is a less difficult approach but not recommended, as you may spend a long time out of ketosis before you find you net carbs limit.
If you can't see any ketones, be patient. It typically takes 2-3 days for your body to deplete glycogen stores, so don't expect to be in ketosis after just a day of low-carb. Remember, ketosis is a favourable condition and an indication that your body uses fat for fuel but you can lose weight even without being in ketosis. Diet high in fat, adequate in protein and low in carbohydrates is naturally sating, making you less hungry and, therefore, help you lose weight.
Why You Should Think Twice Before Going "Zero-carb"
There is no need to go "zero-carb" eating unless you are doing Restricted Ketogenic Diet for therapeutic reasons. Most people experience all the great fat loss and health benefits of the Ketogenic diet at 20-30 grams of net carbs (or up to 50 grams of total carbs) per day. Remember, more ketones won't help you lose more weight. You simply need to find your optimal carbs level to sate your appetite and feel good.
How About Thyroid Issues on a Low-carb Diet?
It's a common myth that low-carb diets cause hypothyroidism. There is no such evidence. Low-carb diets may cause decreased hormone levels but this is not always indicative of a thyroid disease. Instead, calorie restriction is more likely what leads to thyroid issues, especially if it's over a long period of time.
As someone who has hypothyroidism (Hashimoto's), I can confirm that low-carb / paleo diet has not made my condition worse. In fact, it had the opposite effect and my thyroid function has improved. Although I still have to take levothyroxine, I feel better and my antibody values went down. I'm not saying that LCHF eating can reverse hypothyroidism but I'm willing to try and see if it improves my condition even further.
No diet plan fits all and not everybody can follow a very low-carb diet. Even Dr Volek and Dr Phinney noted that there is not enough evidence that a very low-carb diet (such as less than 20 g net carbs) is beneficial for those with preexisting thyroid or adrenal conditions. Dr. Broda Barnes, who spent over 50 years on thyroid research, suggested in his book “Hypothyroidism: The Unsuspected Illness” that the minimum amount of carbohydrate intake for patients with hypothyroidism should at least 30 grams of net carbs.
I personally don't follow a very low-carb diet because I have such a preexisting condition which may have been caused by my calorie-restricting dieting many years ago. My "ideal" level is somewhere at 30-50 g net carbs (light ketosis). By "ideal" I mean a level at which I feel great and maintain a healthy weight. I sometimes eat less carbs out of habit, not because I force myself to follow a very low-carb diet. Eating less carbs doesn't help in my case: it made no difference to my appetite or energy levels but I felt worse. You simply need to try it yourself and find your "ideal" carb intake.
As I mentioned in many of my previous posts, you don't necessarily need to be in ketosis to lose weight or maintain a healthy weight. The main reason people lose weight on a low-carb diet is its natural appetite control. You can find out more about measuring ketones in my post here: Ketosis & Measuring Ketones.