Another year is in the books! And with it, many thousands of new research studies. Here are five important lessons we learned about nutrition, as we scoured the research for you:

1) The sugar industry continues its hijinks

A study dating from December of 2016 suggests that industry-funded sugar research may be more likely to show favorable results for sugar. This confirms something you probably already knew as an Examine.com reader, which is that published research isn’t necessarily true just because it’s peer-reviewed.

The sugar industry has taken ample advantage of this, stretching back to the 1960s when they funded Harvard researchers to help shift the blame for heart disease from sugar to fat. This was just made public in November of 2016 when decades-old internal sugar industry documents were analyzed.

Just one month after that paper, researchers tied to the sugar industry published a massively controversial review. Why was it so controversial? The review said that dietary guidelines, which recommend lower intakes of processed sugar, are flawed and should be eyed with suspicion. You know what else could be eyed with suspicion ...

A review with ties to the sugar industry just happened to conclude that advice to cut sugar is based on flawed evidence. Keep in mind that this review just looked at dietary guidelines, not the actual sugar evidence.

To be fair, high-fructose corn syrup (HFCS) is unfairly demonized compared to table sugar, and recent research showed no difference between HFCS, fructose, and glucose for inflammation and gut permeability; but this isn’t what the above review looked at.

Take a step back and think in simple terms: Weight gain is much easier when you eat a ton of processed foods, whether it’s sugar or flour or something else. And in the vast majority of randomized trials, eating too much sugar is strongly linked to health problems, from heart disease to fat deposits on the liver and other places.

Sugar isn’t “bad”. Fat isn’t “good”. Absolutes are rarely true. You have to look deeply into the hundreds of important trials and mechanistic studies to tease apart these issues.

2) Low-carb isn’t magic for fat loss

Low-carb research is the least fun to write about. Scratch that — it’s super interesting, but without fail we get angry emails from either low-carb or low-fat proponents. Or both.

Here’s a perfect example: In 2015, NIH researcher Kevin Hall put people in metabolic wards, controlling diet and exercise to precisely compare the effects of a lower-carb diet with those of a low-fat diet. Both diets led to an equal amount of fat loss. After we analyzed this study, we got some angry emails from low-carbers. The carb level was sooooo high! (But then, this happens in a lot of studies.) The study was sooooo short! (But then, very long metabolic-ward studies would be prohibitively expensive to conduct.)

In 2016, Dr. Hall performed a follow-up experiment, this time partially funded by a non-profit organization with a low-carb bent. Plus, the carb level was brought down to ketogenic levels. And yet, once again, the low-carb diet showed no fat-loss magic. Predictably, the trial got lambasted by low-carb advocates online — but would they have found any problem with the study’s methods if it had found a fat-loss advantage?

Let’s be fair: Low-carb diets can be a great! Some meta-analyses even suggest that, in free-living situations (as opposed to “life” in a metabolic ward), low-carb diets can lead to greater fat loss than low-fat diets. This advantage, however, isn’t due to the sheer reduction in carb intake — because, as was made clear by the recent studies by Dr. Hall, insulin isn’t the devil when it comes to fat loss. Rather, low-carb diets can support fat loss by narrowing down food options, by helping combat addictions to sweets and processed carbs, and by promoting an increase in protein intake.

Caloric intake, not carb intake, is what really matters with regard to fat loss; so go with a dietary strategy that works for you. The best hypocaloric diet is the one you can stick to.

3) Vitamin D research is more complex than you’d think

Vitamin D is an interesting nutrient. Not just because it’s a hormone precursor, unlike other vitamins, but because the research on it is EXPLODING. And complex.

Sometimes, really positive studies come out, like this one, published in December of 2016, which suggests that vitamin D can help with cystic fibrosis. Yay!

Alas, for other diseases, the evidence is murkier. While taking 800 IU of vitamin D increases blood vitamin levels, it doesn’t seem to improve heart disease markers. Even worse: Both low and very high levels of vitamin D have been linked to heart disease. And to complicate matters further, an “umbrella review” (a meta-analysis of different meta-analyses) concluded that vitamin D research is less reliable than most people think.

The significance of this review is debatable, though. There are dozens of meta-analyses on vitamin D, but with great variations in doses and populations. Sometimes, a meta-analysis can lose too much of the granularity of the individual studies, and this is doubly true for an umbrella review. So an individual high-quality randomized trial can also be quite valuable (this one, for instance, shows that vitamin D can help with major depression symptoms, whereas this one shows improvement in IBS symptoms), especially if the population matches the person who’s interested in applying the findings. Plus, new meta-analyses come out all the time, such as this one showing that vitamin D may help with pain.

But the vitamin D picture is even more complex than that, and not always rosy. Just in 2016, studies came out showing that high doses of vitamin D could increase the risk of falls in seniors, whereas lower doses could promote hypercalcemia.

Vitamin D is the most hyped vitamin of the decade. But the hundreds of randomized trials paint a much more complex picture than you’d think, both of the potential benefits of vitamin D and of its potential side effects.

4) Respect your gut, and your gut will respect you

The gut, and its connections to our brain and other organs, may be the most exciting area of nutritional research today.

For example, did you know that a low-fiber diet could deplete mucous from the walls of your intestines, making it more likely that pathogens will cross into your body? Or that the evidence doesn’t really support the recommendation that gluten be introduced to infants between the ages of 2 and 4 months to reduce their chances of developing celiac disease? Or that roughly 37% of your gut microbiome diversity is due to your genetics?

If you pretend to know everything about gut health, real gut researchers will mock you. For even though new studies on the topic come out all the time (for example, this one on probiotics plus prebiotics helping with eczema), there’s still so much we don’t understand about the gut. For instance, sometimes dead/inactive probiotics show benefit, as in this study reporting that dead probiotics helped with weight loss. And in some people, a probiotic that helps others will lead to major diarrhea. Some people do well with probiotic pills, but poorly with probiotic foods (such as kimchi) because of the probiotic strain differences, some other food component, or another factor. And conversely, of course, some people fare better with foods than with pills.

The gut hosts a complex microbiome and interacts with many other organs. This makes it both unpredictable and a fascinating area of research. As it stands, 2016 has provided us with a ton of evidence to chew on, such as potential benefits for autoimmune conditions and weight loss.

5) There’s soooo much we still don’t know about nutrition

New studies come out each month, adding to our overall knowledge on nutrition. For instance, in the past year, we discovered that obese people have lower vitamin E bioavailability, that nitrate-rich veggies could boost exercise performance, and that cow’s milk is not all the same (milk containing only A2 casein seems to cause fewer digestive problems than “normal” milk with both A1 casein and A2 casein).

Examine.com is, admittedly, a weird website. We say upfront that we don’t know everything, and that everything is subject to change as new evidence gets uncovered. We’re not nutrition gurus, even though we love analyzing nutritional studies. So we’ll stick to the research, and leave it to you to apply (or not) its findings to your life. And if you’d like to get research updates from us, sign up to become an Examine.com Insider below. No spam, just research.