Could also be parasites. Parasites are considered to be among the most common of Lyme coinfections by some LLMD's/LLND's.
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And I also agree about
checking your calorie intake now vs. prior to changing your diet.
Also, most of us don't chew our food enough times before swallowing. Digestion begins in the mouth, with the mixing of the food with enzymes in our saliva. This is particularly important with carbohydrates, but also the food itself needs to be very broken down by the teeth first before sending it along to the stomach. The stomach doesn't have teeth, so large pieces of food can't be broken down easily once swallowed, which means the nutrition in those large pieces won't get digested & metabolized.
White bread, cheese, and other similar "soft, white foods" typical of the "standard American diet" will eventually dissolve in liquid solution, but high fiber healthier foods don't break down well even when wet. Thus the teeth must do more work, so that the enzymes in the stomach and small intestine can get to all the nutrition in the food to enable absorption.
It is also known that Bartonella and Babesia (in addition to Lyme borrelia) can affect gut transit time, either speeding it up or slowing it down. Furthermore, these critters can cause inflammation in the gut, which causes leaky gut, protein loss into the gastrointestinal tract (a marker for inflammation), and malabsorption. All of this can lead to weight loss.
Marshmallow Root, DGL, zinc carnosine, Slippery Elm Bark, okra, L-glutamine are all things you can try for helping to heal the leaky gut. Omega 3 fatty acids (from fish oil) are also very important for healing a leaky gut.
Candida can also complicate this (by making leaky gut worse), as can taking antibiotics that destroy beneficial bacteria in the gut. Probiotics are an important part of restoring health to the gut, but start carefully because a leaky gut can make tolerance of probiotics difficult.