Keep up the good work.
Don't worry, your body is so used to all the sugar from the low fat products that it's probably going through a withdrawal process now. Expect mood swings and cravings for a while, and they'll disappear. Consider yourself a recovering junkie
Seriously, sugar is incredibly addictive.
I agree that this low fat diet is bad for you. From what you describe, you're eating too much processed food. Highly processed food is poor in both nutrients and essential bacteria.
I'm not sure your friend's diet is the perfect diet either. There are a lot of health problems related to these high fat, high protein diets. Also, protein shakes? Not great for your liver.
There is so much junk science out there when it comes to nutrition, mainly because nutrition is a very complex field, and studies tend to look at isolated areas of nutrition, meaning that they can be simultaneously correct and completely useless for all practical purposes.
If there is one thing I could recommend you, it's to read one of Michal Pollan's books on food, particularly In Defense of Food or Food Rules. What is so great about them is that they look at diets from a historical perspective, explore food traditions and weaknesses in nutrition science. One of Pollan's points is that humans have developed food traditions over centuries, and that they have good reasons for being the way they are.
As for the energy in - energy out formula, it's an oversimplification. A Danish study published in Journal of Obesity found that people with high levels of Prevotella bacteria in their gut lose weight much easier than people with high levels of Bacteroides bacteriea. A quick google search found that Prevotella bacteria is more common in people who eat a highly plant based diet - which was the common diet almost everywhere on the planet a 150 years ago.
And yes, having a high stress job like yours makes your body cling on to its fat for dear life.
Sugar is the worst though. It's linked to just about every possible health problem imaginable. Sarah Wilson has an interesting diet/cookbook called I Quit Sugar. There is a web site as well. She is pretty neurotic and cites a lot of questionable studies in her pursuit of a sugar free lifestyle, but what is great is the step by step system for eliminating sugar from your diet. What makes her believable is that she quit sugar in order to manage a nasty thyroid condition, and it seems to be helping.
This became a text wall, but the issue is complex, and just pursuing weight loss without considering other health aspects is damaging. I think educating oneself on nutrition is a life skill that is necessary in the modern world.
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I sometimes leave conversations and return after a long time. I am sorry about it, but I need a lot of time to think about it when I am not sure how I feel.