It probably doesn’t come as too much of a surprise to you that in the United States almost 40% of adults over 20 are considered obese and over 70% are considered overweight. In the world, 13% of adults over 18 are obese and 39% are overweight. While activity levels do play a role in weight gain, it largely falls back on eating too much. It’s an interesting dichotomy when people are eating way more calories than they need, but are still not getting enough of many essential nutrients.
Regardless of the type of diet you’re following, it’s very possible that you’re experiencing some form of vitamin deficiency. Different types of diets do pose different challenges and that’s all the more reason to be mindful of what you’re at risk for. For example, 80-90% of vegetarians/vegans are Vitamin B12 deficient. That is an alarming statistic that just goes to show that people don’t do enough research before changing the way they eat. The fact that vegans must supplement B12 is well known. In fact, it’s one of the first things I learned about veganism. Point being, the information is there, you just need to look for it. You need to care enough to bother.
Other common vitamin deficiencies among people with a range of diets include: Vitamin D, iron, iodine, calcium, magnesium, and Vitamin A (in developing countries). There are many factors outside of diet such as gender, age, and race that can play a role in what deficiencies you may be at risk for.

I’ve believed for a long time that people essentially know how they should eat, but they just don’t want to (myself included). I no longer believe that. Perception can be tricky. There’s so many different ways to eat and an abundance of anecdotal evidence to support each of them. I do believe there is an inherit common sense that most of us possess that tells us things like, “fast food is bad for you” or “salad is good for you”. But doesn’t even that get convoluted? Is a salad with no protein or healthy fats, but a caloric sugary dressing still good for you? Some people argue that a burger from McDonald’s is perfectly healthy as long as you skip the bun. Let’s be honest, many people make deliberately unhealthy decisions, but that doesn’t change the fact that it’s more confusing than ever to know how to eat.
I’m someone who has struggled with my weight my entire life. Switching to veganism was not about losing weight for me, but that is another factor that shapes the way I’m trying to eat. I recently downloaded an app on my phone called Cronometer. It’s one of those things where you can input what you eat and it will tally up the calories and whatnot. However, it also breaks down the vitamins that you’re getting. Not everyone wants to track what they eat everyday and I understand that. However, for some people it can be a wonderful tool to show them the reality of how their food choices may be lacking. For me, focusing on individual nutrients and not just calories has been eye-opening. I’m not looking to follow a fad diet or some lose weight quick scheme. All I want is to give my body the nutrients it needs while not overloading it with a bunch of stuff it doesn’t.

Sources:
https://www.healthline.com/nutrition/7-common-nutrient-deficiencies#section7
https://www.cdc.gov/nchs/fastats/obesity-overweight.htm
https://www.who.int/news-room/fact-sheets/detail/obesity-and-overweight