If you are fairly new to a low carb diet, and are feeling a bit ropy right now, here are some pointers to consider:
There are a few factors to consider here, some to do with general body chemistry, and some specific to changing to low-carb.
Firstly, if you are too drastic when you initially start a diet (of any sort) your body will react by trying to stop you. It wants to maintain Homoeostasis, and keep you alive.
You know that you are wanting to drop fat and get more healthy, but initially, your body sees any change as a bad thing. It will want you to give it what it is used to if you can, and signals its discomfort loudly.
Secondly, and specifically to low-carbing, you are in sugar withdrawal. Even if you didn’t eat lots of sugar to start with, your body chemistry breaks down all starches into Glucose (the simplest sugar there is) and uses it for fuel. Because you’ve removed your body’s fast fuel fix, again, it’s going to protest!
Your body is conditioned by food intake, and in our carb-centric world, this means maintaining fat stores and use dietary glucose. It takes around 3-5 days for your body to register that it’s not going to be getting masses of fast-burn glucose again any time soon and so gives in and starts to pull fat from fat stores and use ketones for energy full time. Note that everyone burns ketones from their own fat overnight, if we hadn’t evolved this body mechanism, we’d have to either eat constantly or die.
Meanwhile, because your body doesn’t actually like using up its fat stores unless it has to do so (during “the lean of winter” etc.), and has been very happily expecting and using sugar as fuel, it screams at you to give it back the fat building and preserving fuel that it’s been used to running on.
These two factors combine to make you feel rotten for a week or so. Your body doesn’t like change, and it tells you so 😉 You can mitigate these feelings by taking on electrolytes, as they are being flushed out with your the water your body is using and excreting as your Glycogen stores are burned through. Replacing Sodium, Potassium and Magnesium is the key. Try some gherkins, drink some good quality ready made stock/broth, make Stock cube or BovrilTM drinks and use salt (preferably Himalayan) on your food.
However, Ketones are your heart & brain preferred energy source, not Glucose (Sugars and Starches) and by proving to your body that food is plentiful, via eating lots of fat and protein with green veg and a broad range of other nutrient loaded low-carb plant products, your body will down-regulate Insulin (fat-storing hormone), up-regulate Glucagon (fat-burning hormone) and Leptin (Appetite suppressant hormone) wins out over Ghrelin (Appetite increasing hormone).
Once your hormones are rebalanced, your body will establish a new level of homoeostasis and stop protesting. And that means you are well on your way back to the body that Homo Sapiens evolved to have.