Something that doesn't get talked about enough with regard to diet and fitness: the effect it has on our mental state. Especially during the first few weeks.
Starting a new diet or new fitness routine can be really disruptive to your mood and energy levels. And it makes sense if you think about it: your routine has been disrupted, you're taking in fewer calories and burning more, and your hormone levels are changing as your endocrine system tries to compensate. Until things stabilize, you'll be more tired, hazy, uncomfortable, and "hangry." It can take several weeks.
I feel like most people expect to have sore muscles and food cravings, but the irritability, depression, anxiety, mood swings, and difficulty concentrating all come as a surprise.
So just a quick reminder for folks making a fresh start in the new year: if your mood or your mental health has been in shambles this past week, or if you've been feeling "down" or "a bit off," it might be your metabolism going haywire. Try adding a few lean calories (like a glass or two of tomato juice) to your diet, and a half-hour of good, deep stretches (or yoga) to your routine, and chat with your mental wellness professional if it doesn't help.
(And as always, check with your doctor before starting any diet or fitness routine.)