Quick preface: I have taken one university food science class and read the US government's ~200 page meta study that they publish every five years to summarize the best scientific research on diet and nutrition. It's actually a good read. I am NOT a dietician.

For peak health your body needs a minimum quantity of water, fiber, protein, carbohydrates (yes, carbs), minerals, vitamins, fats - even cholesterol - and other nutrients to remain healthy. The best way to digest all of those nutrients is as part of whole foods which come with calories. For a grown man your nutritional requirements cannot be met without consuming >1500 calories. That is why you should aim to lose no more than ~1 pound per week if you are focusing exclusively on calorie deficits / restriction.

With diet and exercise you - arguably - should not lose more in total than 1.5 to 2 pounds per week. When you exercise strenuously your nutrient requirements also go up. Your body needs some accessible energy that only comes with carbohydrates. If you are exercising a lot your body needs additional protein to make up for the breakdown you are causing to your muscles. Fiber is critical for a balanced diet. I know some dieticians that feel pretty strongly that the number is closer to 1lb than 1.5 lbs per week, particularly if you care about performance.

I am a huge advocate of food journaling (measuring the amount of food you eat and writing it down & at some point within a 24-48 hour period doing a fast google search on how much you eat). If you right it down in a Word, Excel or Google Doc it won't be long until you already have a ready resource to quickly calculate how many calories you eat. I actually like it much more than myFitnessPal because by the time I found &/or adapt their database entries I usually can quickly find the answer myself.

I take the counsel in Doc. & Cov. at face value ('words of wisdom' or advice) that whole grains and herbs (1832 definition: vegetables) are to be the 'staff of life' (foundation of your diet). Yes, carbs, vitamins and minerals, and fiber. I think most fad diets have some initial shock value because they cause people to limit their calories whenever they radically alter their diet to 'no carbs' or keto or whatever. In the long-term, it's all about calorie intake vs. consumption. If you don't understand & address why you over-eat on a non-keto diet you will eventually learn how to overeat on a keto diet.

Health requires a variety of nutrients that includes carbs, fiber, etc and a sparing intake of saturated fat. People don't drink enough water and depend too much on food to meet their fluid requirements. While I am a huge advocate of food journaling - particularly when you are outside your target weight range - I am also a big believer in not freaking out about small data points. The trend is what matters. It's still okay to enjoy a holiday dinner with family, a pizza night with the kids or that one favorite dessert that you like. But it needs to go in your journal (whatever works for you) and then placed within your week of food consumption and understood within your trend.