Dairy is one of those food groups that the nutrition community just does not seem to be able to agree on. Some people love it, some people think we should never consume it, and others are somewhere in the middle. I'm not going to lie, for a long time I was in the "I don't think humans were ever meant to consume dairy" category, and while my logic was based in some sound reasoning and research, these days there are few foods I would choose to take such a polarized stance on. Now my stance on dairy consumption is 100% based on the needs of the individual, and thinking about what is best for the environment.
why you may want to/need to avoid dairy products
Like everything in nutrition, whether to consume, or not to consume dairy products really does come down the the individual. While some individuals physically are not able to consume dairy products, others may choose not to due to the way dairy reacts in their bodies, or for personal/religious beliefs.
Here are just a few of the reasons why some people may want to avoid dairy products:
For some people and specifically in some cultures, dairy just is not digested well, and for these people it may be best to be avoided. For instance, in Asian, African American, and Native American populations research has found that roughly 80-100% of the population may have some degree of lactose intolerance. This means that overtime these cultures never developed enough of the lactase enzyme that is required to digest milk products. It also is not a surprise that these cultures have very little traditional dishes which include high-lactose dairy products, and so today have very little tolerance to dairy when consumed. 
For those who are lactose intolerant, there are however many diary options that are naturally lactose free such as most hard cheeses like parmesan, and aged cheddar. Additionally fresh buffalo mozzarella is also naturally lactose free, as is ghee for a butter alternative.
Additionally, I love the brand Green Valley Organics, which makes incredible organic lactose free dairy products that is absolutely worth trying.
Irritable bowel syndrome
For many individuals diagnosed with IBS, dairy products can be an issue for an already poorly functioning GI tract. Lactose (the sugar found in milk) is considered to be a FODMAP, which are a group of sugars that have been found to cause significant discomfort in people with IBS.
If you are someone who has been struggling for years with IBS it may be worth finding a registered dietitian who specializes in GI concerns. Most likely your dietitian will recommend trialling a lactose free diet for a few weeks, and then slowly reintroducing lactose containing foods to determine whether or not they are a trigger for you.
With time, and healing of your gut, many people are capable of enjoying lactose containing dairy products again, but they may just need to take a bit of a break for a little while to identify what their IBS triggers are, and how much their bodies can handle.
Other people may simply be allergic to Milk, which is one of the top 8 allergens and can cause GI issues, skin rashes, and anaphylaxis. This is usually due to an allergic reaction to the proteins whey and casein found in milk products. The good news however, is that Milk is one of the most common pediatric allergys to outgrown, and in about 90% of cases the allergy is outgrown by adulthood.
One of the first things I do when someone has an auto-immune condition (such as MS for instance) is place them on an auto-immune protocol, which basically consists of a reduction in foods known to cause inflammation, and an increase in foods that are known to decrease inflammation.
Dairy is one of those foods that especially for people with auto-immune or other inflammatory conditions may need to be avoided for a period of time, and reintroduced in moderate amounts, or not at all depending on the results the individual experiences.
However, it is important to note that while some dairy products, especially those which are not organic or grass fed, may cause increased inflammation in certain individuals, it also has been found that fermented dairy products like kefir and yogurt actually have anti-inflammatory properties and benefit a healthy, functioning GI tract. So when it comes to dairy, the quality and type of product really is so much more important when deciding whether or not to include or exclude it from the diet. 
chronic skin conditions such as rosacea, acne, dermatitis
Similar to auto-immune disorders, some people with inflammatory skin conditions may also benefit from a reduction, or elimination of dairy from their diet. For some people this solves their skin concerns, while for others it may not be the associated trigger. However, if I have a client who is really struggling with skin concerns and has not trialled a dairy elimination diet we always start there.
so why should you add full-fat dairy products into your diet?
With all these reasons why people may want to consider removing dairy from their diet, there are also many reasons why it could be a good idea to add it in!
For starters, if you are choosing an organic, grass fed, full-fat dairy product, you are choosing to include a food in your diet that contains high levels of omega-3 fatty acids and other healthy fats, which will help protect your heart and help promote hormone balance.
Additionally, many high quality dairy products are excellent sources of protein, which can be great options especially for individuals who choose not to consume meat. With roughly 15g of protein in 8oz of greek yogurt, this is an excellent healthy option to add into your diet. Just make sure you opt for the unsweetened varieties!
Lastly, in a large Nurses Health Study II out of Harvard, women who consumed >1 serving of a full-fat dairy products per day was found to have a decreased risk of anovulatory infertility when compared to women who consumed low-fat diary products. So if you are thinking about your fertility, and are hoping to grow your family in the near future, it wouldn't hurt to add some high-quality full-fat dairy products in as a fertility boosting snack.
what to look for when choosing a high-quality dairy product
- Choose Local: Above all else, always opt for local milk, cheese, and yogurt products. Many farms are unable to afford the organic certification, but it honestly doesn't matter because there is nothing better than meeting your local farmer and learning to trust and put a face to the people providing food for your family. Not to mention, shipping dairy products has a high carbon footprint due to the refrigeration required to ship. For all these reasons purchasing local will always be the best option. To ensure that your local farmer follows healthy farming practices that you can trust and believe in, when talking to your local dairy farmer always ask these four questions:
- Are your animals treated with antibiotics?
- Are your animals grass fed? How are they treated?
- Are your animals ever treated with growth hormones, for example rBGH is a common hormone used.
- If purchasing raw dairy products: What are your sanitation standards/practices to avoid food borne illness.
- Go for Organic and Grass Fed: After local, choosing an organic dairy option from within your region is your next best thing. When you choose organic, you are choosing a dairy product from an animal that has never been treated with antibiotics or growth hormones. Ideally you would also choose a grass fed option, which is going to ensure that the dairy product has higher levels of heart healthy omega-3 fatty acids due to the grass it was feeding on.
- Opt For Unsweetened: Just because your yogurt says organic, doesn't mean a good amount of sugar hasn't been added to the yogurt to make it taste sweeter and less tart. Instead opt for the unsweetened versions and choose to add your own fresh berries and nuts for a more balanced, healthy snack.
Ultimately whether you choose to include, or exclude dairy in your diet, just make sure the reasoning is specific to your body and your lifestyle. Dairy can be a really wonderful and healthy addition to your diet if it supports how your body was meant to function. My recommendation for everyone however is to consume dairy in moderate amounts, choose products that support the health of our environment, and pay attention to your own body...not the latest headline.
 Itan, Y., Jones, B. L., Ingram, C. J., Swallow, D. M., & Thomas, M. G. (2010). A worldwide correlation of lactase persistence phenotype and genotypes. BMC evolutionary biology, 10(1), 36.
 Bordoni, A., Danesi, F., Dardevet, D., Dupont, D., Fernandez, A. S., Gille, D., ... & Shahar, D. R. (2017). Dairy products and inflammation: a review of the clinical evidence. Critical reviews in food science and nutrition, 57(12), 2497-2525.