Nutrition is a science, not an opinion. Registered dietitian nutritionist (RDN)* – trusted nutrition expert

nutrition science

In addition to my nutrition coaching business, I love to teach and have been an adjunct professor teaching Principles of Nutrition since 1998. People don’t realize that nutrition is a science.

I encourage communication in the classroom, my students don’t hesitate to ask questions. I don’t always have the answers, but I’m committed to finding out what’s known and new in the field. For example, a while back a student asked about oil pulling. What? I had never heard of it. I thought she was joking when she explained what it was.

You put about a tablespoon of edible oil, like sesame or coconut oil, in your mouth, swish it around and pull it between your teeth for up to 20 minutes before spitting it out. Supposedly it pulls toxins from your mouth. Oil pulling is an ancient Ayurvedic ritual with many believers and considerable anecdotal support. Actually, there is some scientific evidence it may reduce plaque and gingivitis, as reported in the Indian Journal of Dental Research. However, the American Dental Association does not recommend this practice (see ADA article). As far as removing toxins, I find no credible evidence it does.

The field of nutrition is ever evolving

The world of nutrition is so vast it’s impossible to know everything. Being the young science it is, the field of nutrition is ever evolving. It’s challenging without a doubt. But, as a registered dietitian nutritionist, it’s my responsibility to stay up-to-date on the science and evidence. For example, I’ve watched common household products go from the “healthful” status list to the “bad for you” list.

Back in the day, margarine was thought to be a better alternative to butter because (a) it was made from a vegetable Stick of butter - quarter pound of fat bestoil, and (b) it did not contain cholesterol. What we have since learned is that in order to make vegetable oil spreadable (into margarine), it had to go through a process called hydrogenation, ultimately creating trans fats, which we now know are especially harmful. (They not only increase the LDL “bad” cholesterol, but decrease the HDL “good” cholesterol.) We also have learned cholesterol is not the culprit in increasing risk for heart disease, as we once thought.

The good news is we now can avoid trans fats and know in which foods they hide. Due to the 2006 change in the nutrition labeling law, all Nutrition Facts panels are required to list trans fats. As a result, food manufacturers found alternative means to processing, and billions of pounds of trans fats were removed from the food supply. Few margarines (and foods) now contain trans fats.

Do I regularly recommend butter over margarine or vice versa? Not necessarily. I actually recommend liquid oils like olive or canola oil. But this brings me to another point. Everyone is an individual and what may be appropriate for one person may or may not be appropriate for another. I may recommend butter to one person but not to everyone.

Nutrition? How hard can this be?

Interestingly, I went back to school to study nutrition because I was confused. I had always had more than a passing interest in nutrition. Prior to my return to school, I read everything related to nutrition.

Yet one day I would read or hear what one supposed expert would say and think, Well that sounds reasonable, only to hear something totally contradictory the next day. What to believe?

I made a life-changing decision and decided to go back to school. Initially, I thought, Nutrition? How hard can this be? Oh how wrong I was.

My coursework the first semester back to school was:

  • Anatomy & Physiology (with lab)
  • Inorganic Chemistry (with lab)
  • Microbiology (with lab)
  • Principles of Nutrition

Nutrition is biochemistry

That was just the beginning. That much science? Yes. Nutrition is biochemistry—the chemistry of living things. Do you ever think of what happens when you take a bite of food? Nutrition is about that bite of food—the protein, carbohydrates, fats, vitamins and minerals—and the digestion, absorption, transport, and metabolism of the nutrients. Pretty cool stuff. To me anyway—but, I’m a nutrition nerd and it’s my life.

Everything in our body was once something we consumed or made within—the bones, muscle, fat, hormones, enzymes, and antibodies. The human body is amazing. People don’t give the body enough credit. It does miraculous things—all on its own.

Because there is so much science behind what guides us—registered dietitian nutritionists—as we help others with their diet and lifestyle choices, I urge people to watch out for baseless nutrition advice they may read online or hear from people not in the field.

Nutrition is much more than calories and food labels, or short news articles based on a new study or idea about food and health. Nutrition is a science—built on the foundation of anatomy and physiology, biology, chemistry and especially biochemistry.

bi·o·chem·is·try – bīōˈkeməstrē/ noun

the branch of science concerned with the chemical and physicochemical processes that occur within living organisms

My students’ eyes light up when I tell them the first day of class—yes, you are going to be learning biochemistry this semester. It might be baby biochem; nonetheless it’s what nutrition is.

Unfortunately, people don’t want to know how complex nutrition is. They want easy answers. So when they hear carbs are bad and should be avoided or gluten is the reason for all our ills or dairy is the devil or animal products are evil, from whatever platform of media or from preaching by people they know, they hold on to that.

Our body needs carbs

Carbohydrates are not bad. Their primary function is to provide energy to cells. They break down to glucose (sugar) in the body—regardless their source. All plant-based foods are sources of carbohydrates. If it came from the earth, it’s a carb. The milk sugar, lactose, is also a carb, so milk and yogurt are carbs as well.

Our body needs carbs. However it’s the type of carb that’s important.nutrition science

Sources of carbohydrates include:

  • Starch/complex carbs – including bread, cereal, whole grains, beans/legumes, pasta, rice, and starchy veggies like potatoes, peas, corn, winter squash and parsnips
  • Veggies, non-starchy – all other veggies not listed above. These foods have a very high water content, over 90 percent water. Because of their high volume of water, a much greater quantity can be consumed relative to starches. There is a ratio of about 4 to 1—of calories you can consume from starchy to non-starchy veggies. Eat away!
  • Fruits – fresh, frozen, canned in its own juice, dried, 100% fruit juice
  • Milk and yogurt – preferably nonfat/skim or 1% milk, nonfat or low fat Greek yogurt, or nonfat or low fat regular yogurt

Of course anything containing sugar or refined white flour is also a carbohydrate source—pies, candy, cakes, cookies, ice cream, sugar-sweetened beverages, etc.

Sugar comes in many forms—brown sugar, corn sweetener, corn syrup, dextrose, evaporated cane juice concentrate, fruit juice concentrate, glucose, high fructose corn syrup (HFCS), honey, invert sugar, malt syrup, maltose, molasses, raw sugar, sucrose, syrup, agave nectar, etc.

The natural sugar in carbs is fine—from fruit and milk. It is the added sugar, noted above, in the diet, when consumed in excess, that should be limited.

Recommendations from the American Heart Association are for women to consume less than 6 teaspoons of added sugar per day (about 100 calories or 24 grams) and men no more than 9 teaspoons or 36 grams. This does not include naturally occurring sugar from fruit (fructose) or milk (lactose).

The updated 2015 Dietary Guidelines for Americans recommend no more than 10 percent added sugar, which is about 12 teaspoons (50 grams) in a 2,000 calorie diet.

According to the Proceedings of the National Academy of Sciences, women consume an average of 15 teaspoons (about 60 grams) of added sugar per day and men consume an average of 21 teaspoons (84 grams). We’re consuming too much!

People with diabetes need carbohydrates. However because of the effect of carbs on their blood glucose, they need to be more aware of their intake and monitor their blood sugar levels on a  day-by-day, meal-by-meal basis for optimal glucose management.

Another area of confusion

Gluten is another area of confusion. A person with celiac disease must be on a gluten-free diet; there is no cure. People mistakenly believe going “gluten-free” is healthier. In some instances it is. Gluten is a protein found in wheat, barley, and rye.

If a person’s diet consists of a lot of white refined flour—white bread, sandwiches, pizza crust, fast food, sweets, cookies, etc. (which contain gluten)—and they go gluten-free, eliminating all those foods, sure they’re going to feel better. Not because of the magic of a gluten-free diet, but because they’ve eliminated a huge amount of highly processed foods and are likely eating more nutritious food.

See Dear Gluten-Free Dieter and Gluten-Free: The Real Reason it Might Help for more info on gluten.

The goal of what I do and how I work with clients is not to apply a cookie-cutter approach to everyone but to work individually with each client. Together, in partnership, my clients and I determine what works, through nutrition principles and an individualized approach—one step at a time.

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* In 1998 I obtained the credential registered dietitian (RD). In 2013 the addition of nutritionist was formally added to that title—registered dietitian nutritionist (RDN). Our profession has the choice to use RD or RDN.

Jennifer Neily, MS, RDN, LD, FAND
Registered Dietitian Nutritionist | Wellcoach® Certified Health Coach


  1. Vincent

    A very informative post and a good read :)

    • Neily

      Appreciate your kind words Vincent! :)

    • Barbara Hunt

      Wonderful article and very informative…have been concerned about so many people striving for zero carbs..

      • Neily

        Excellent – thank you Barbara. Glad you found the information helpful! -Neily

  2. mom


    • Neily

      Thanks mom – you’re the best ;)

  3. Nutrition a la Natalie

    I love the education on carbs. I’m so tired of telling people how important carbs are!

    • Neily

      Very much appreciate your thoughts about that…it was a lot of info.

  4. Angela Lemond

    Well done once again from Jennifer Neily – reliable expert!!

    • Neily

      Thanks Angela! Appreciate the work you do for our profession.

  5. hungryhobby

    Great post thanks for sharing!

  6. Heidi storm

    Hi and thank you for your excellent review. My chiropractor gives me nutrition advice. How much nutrition training do they get. They are doctors and not dietitians.

    • Neily

      I cannot speak to your situation Heidi because it varies amongst practioners. I’ve known some amazing ones and some not so amazing ones. I subscribe to The Tufts University monthly health letter and very much enjoy it because of its evidence-based information and no advertising. Thanks for your question!

  7. AZT

    Great post.. Thank you. However, I don’t think the non-fat/skim or 1% fat dairy is a good advice. There is no evidence for this form is better than whole milk. The main message is eating everything in small amounts and avoiding the processed food as much as possible.

    • Neily

      Thanks for your comment – glad you like the post. I respectfully disagree about the milk. Nonfat/skim milk/1% contain ALL ingredients of whole milk minus the fat. It totally depends on an individual’s diet whether or not to consume skim, 1%, 2%, our whole milk. Personally since I drink a lot of milk – AND I’ve been drinking nonfat milk for as long as I can remember – that’s my preference.

  8. Donna

    Good information Neily! I am a wellness educator and promote whole foods. The benefits that plant based foods have on the system is incredible. I wish more people would add better nutrition to their diets so that they would be able to live a healthier life.

  9. June

    Great article. I first saw “oil pulling” on the Dr. Oz (figures) show on ways to detox your body, only he would promote such nonsence.

    • Neily

      Thanks for your comment June – yes I know…crazy!


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