I'm usually not a fan of the term "superfood." I think it tends to confuse people about which foods are best and how much they should consume. For instance, the ADA's Diabetes Superfoods list includes citrus fruit, whole grains, sweet potatoes, and fat-feee milk. While those items may have beneficial nutrients, their effect on blood glucose levels should instantly disqualify them for consideration on such a list. But I have five favorite foods that I think could be classified as "superfoods." In addition to providing numerous health benefits, they're also very low in carbohydrates and delicious -- an ideal combination.

Cinnamon
 This fragrant spice is prized for its strong, distinctive taste and suitability for both sweet and savory dishes. Although research on its ability to improve insulin sensitivity has found mixed results, many people report lower fasting blood glucose levels as a result of taking 1/2 to 1 tsp per day.

Potential benefits: 

• Lower postprandial blood glucose levels
• Improved insulin sensitivity
• Decrease in LDL-cholesterol levels
• Improvement in liver function, insulin resistance, and inflammation in those with fatty liver 

I like adding cinnamon to coffee and tea with a little half-and-half and sweetener. For an exotic main dish, check out Vanessa of Healthy Living How To's recipe for Cinnamon Braised Beef.

References:

1. Magistrell A, et al. Effect of ground cinnamon on postprandial blood glucose concentration in normal-weight and obese adults. J Acad Nut Diet 2012 Nov;112(11):1806-9 
2. Ascari F, et al. Cinnamon may have therapeutic benefits on lipid profile, liver enzymes, insulin resistance, and high-sensitivity C-reactive protein in nonalcoholic fatty liver disease patients. Nutr Res 2014 Feb;34(2):143-8.

Cocoa

Chocolate has been getting a lot of good press lately. Of course, we're not talking about Reese's peanut butter cups and Hershey bars; dark chocolate with at least 85% cacao is the type to choose for maximal health benefits with minimal nonfiber carbs.


Potential benefits: 

• Improved gut health due to its prebiotic properties
• Decreased oxidation of LDL cholesterol
• Lower risk of cardiovascular disease 
• Protection from sun damage and overall improvement in skin quality

I like unsweetened chocolate, but it's taken me a while to get to that point. For anyone interested in a low-carb version of one of the most popular candy bars of all time, Carolyn of All Day I Dream About Food has created a sugar-free Chocolate Peanut Butter Cup. And Bill Lagakos of Calories Proper shares an incredibly easy recipe for homemade chocolate at the end of a fantastic blog post about the beneficial effects of chocolate and medium-chain triglycerides on liver health.

References: 
1. Tzounis X, et al. Prebiotic evaluation of cocoa-derived flavanols in healthy humans by using a randomized, controlled, double-blind, crossover intervention study. Am J Clin Nutr 2011 Jan; 93(1):62-72 2.West SG, et al. Effects of dark chocolate and cocoa consumption on endothelial function and arterial stiffness in overweight adults. Br J Nutr.2014 Feb;111(4):653-61
3. Ibero-Baraibar I, et al. Oxidized LDL levels decreases after the consumption of ready-to-eat meals supplemented with cocoa extract within a hypo caloric diet Nutr Metab Cardiovasc Dis 2014 Apr; 24(4):416-22 
4. Heinrich U, et al. Long-Term Ingestion of High Flavanol Cocoa Provides Photoprotection against UV-Induced Erythema and Improves Skin Condition in Women. J Nutr 2006 Jun;136(6):1565-9

Avocado


Technically a fruit, the avocado contains high levels of healthy monounsaturated fat, and its carbohydrates come primarily from fiber. In addition, avocados are one of the best sources of potassium around and highly satiating due to their high fat and fiber content.  



Potential benefits: 

• Reduced blood glucose levels
• Protective effect on liver, kidneys, and pancreas

• Antimicrobial activity that could provide an alternative to antibiotic therapy in the future
  
• Inhibition of cancer cell growth

Guacamole is my favorite way to eat avocados, but this Paleo-Stuffed Avocado from Martina at KetoDiet App sounds delicious and contains another low-carb "superfood": sardines. 

References:
1. Ezijiofor AN, et al. Hypoglycaemic and tissue-protective effects of the aqueous extract of persea americana seeds on alloxan-induced albino rats. Malays J Med Sci 2013 Oct;20(5):31-9 
2.Guzman-Rodriguez JJ, et al. Antibacterial activity of defensin PaDef from avocado fruit (Persea americana var. drymifolia) expressed in endothelial cells against Escherichia coli and Staphylococcus aureus. Biomed Res Int 2013; 2013:986273
3. Ding H, et al. Chemoprotective characteristics of avocado fruit. Semin Cancer Biol 2007 Oct;17(5)386-94

Sardines and Herring

Sardines and herring are generally love-or-hate foods, but those of us who enjoy them definitely have the edge in reaping several health benefits. Their omega-3 fats and low mercury content make them a natural choice for "superfood" status.


Potential benefits: 

• More favorable omega-6:omega-3 ratio as a result of high DHA and EPA content
• Reduced risk of cardiovascular disease
• Improvement in bipolar disorder and other forms of depression
• Reduced frequency and size of colonic polyps

Fortunately for me, I love both of these. I usually eat sardines about three times a week for breakfast with cucumbers, cherry tomatoes, olive oil, and vinegar. For a fancier presentation, try these Romaine Wedges with Sardines and Caramelized Onions from the Eating Well website.

Reference:

1.Richard D, et al. Infusion of docosahexaenoic acid protects against myocardial infarction.Prostaglandins Leukot Essent Fatty Acids 2014 Apr;90(4):139-43 
2.  Grosso G, et al. Omega-3 fatty acids and depression: scientific evidence and biological mechanisms. Oxid Med Cell Longev 2014;2014: 313570 
3. Hull MA. Omega-3 polyunsaturated fatty acids. Best Pract Res Clin Gastroenterol 2011 Aug 25(4-5):547-54 

Eggs
Eggs really are the perfect low-carb choice for any meal. Isn't it nice that one of the healthiest foods around is also one of the most versatile? Of course, we should all be eating the yolk, its most nutritious part. In addition to containing protein of the highest biological value (meaning our body uses it more efficiently than protein from any other source), eggs keep us healthy in several ways.


Potential benefits:

• Provide important nutrients like choline (vital for the brain), vitamin K2 (for heart and bone health), and the antioxidants lutein and zeaxanthin (keep eyes healthy and free from macular degeneration)
  
• Raise HDL cholesterol ("good" cholesterol)
• Promote a shift from small, dense atherogenic LDL (Pattern B) to larger LDL (Pattern A)

My favorite way to eat eggs is sunny-side-up over sautéed kale with sea salt. I think they'd also be fantastic in this recipe for Eggs Baked in Tomato Sauce. 


References: 
1. Nasopoulou C, et al. Hen egg yolk lipid fractions with antiatherogenic properties. Anim Sci J 2013 Mar;84(3):264-71 
2. Handelman GJ, et al.Lutein and zeaxanthin concentrations in plasma after dietary supplementation with egg yolk. Am J Clin Nutr 1999 Aug;70(2):247-51
3. Fernandez ML. Effects of eggs on plasma lipoproteins in healthy populations. Food Funct 2010 Nov;1(2):156-60 

So while we can argue about whether there truly are any "superfoods," I think you can see why I feel the foods above should have a prominent role in your diet. Try to get at least a couple in every day.

One of the things I see time and again is people going heavy on the protein and fats while avoiding most vegetables and fruits when following a low-carb diet. While you're  definitely minimizing carbs by only eating meat, fat, and leafy greens, you're also missing out on the benefit of including a large variety of plant foods in your diet. 

Acid Base Balance
One concern regarding carbohydrate restriction is its adverse effect on the acid-base balance in the body. A high intake of acidic foods (primarily animal proteins) can result in loss of calcium in the urine and an increased risk of bone loss. This fact is often pointed out by advocates of vegan or plant-based diets.  Protein plays an important role in appetite regulation and satiety, as well as performing many vital physiological functions. Compared to plant proteins, animal protein is both complete and of higher biological value. But at what level of protein intake does calciuria occur? Researchers found subjects to be in negative calcium balance on diets containing around 100 grams of protein per day, which isn't hard to exceed on a low-carbohydrate diet, or even the standard American diet. However, increasing intake of alkaline foods like vegetables and fruits has been shown to improve acid-base balance and significantly decrease urinary calcium losses. Adding plant sources of calcium (green beans, broccoli, greens, cauliflower, carrots, and oranges) would strengthen  this effect.

Fiber
Many low-carb advocates downplay the importance of fiber in the diet. While its cholesterol-lowering properties have proved to be less dramatic than once believed (who can forget the oat bran craze about 20 years ago?),  there's new evidence that it may be quite beneficial for people with diabetes or prediabetes. Researchers looked at 15 studies conducted over a span of 30 years and concluded that increasing dietary fiber consumption by an average of 18 grams per day lowered fasting blood sugar by an average of 15 mg/dl, a significant amount. Of course, we are all unique in our response to nutrients, so not everyone who increases their fiber will experience the same results, but these results are encouraging. I find it particularly interesting that the fasting value rather than the postprandial value (which wasn't measured, as far as I can tell) decreased. The Hgb A1c also improved, but only fell by an average of 0.26%. However, since many of the studies were of relatively short duration and A1c is typically measured every 12 weeks, the actual improvement in long-term control may well have been greater.

Some of us tend to overestimate the amount of fiber we get.  I recommend shooting for at least 30 grams a day, but more is even better. Here's a user-friendly online calculator to determine your total fiber intake for the day. I had 40 grams yesterday from vegetables, fruits, and nuts as part of a total carb intake of 106 grams (66 net carbs for the day). 

Phytochemicals
Perhaps the most important reason to eat a wide variety of produce is the many types of phytonutrients (literally "plant nutrients") they contain. The color or pigment of a fruit or vegetable determines its type and potential benefits. The list of phytochemicals, their properties, and the plants that contain them is extensive, but here's a quick overview of a few of them:
Sulforaphane, isothocyanate, and indoles found in cruciferous vegetetables (broccoli, cabbage, kale, and Brussels sprouts) have been shown to protect against cancer.
Lycopene is found in tomatoes, grapefruit,  and watermelon. Its consumption is linked to decrease incidence of certain types of cancer, including prostate cancer.
Anthocyanin-containing foods include berries, plums, red grapes, cranberies, and pomegranates. Protection from cancer and reduction in inflammation are attributed to this red/purple pigment. 
Carotenes/carotenoids are found in carrots, pumpkin, apricots, cantaloupe, and yams. Properties including decreasing inflammation by quenching free radicals and assisting in the communication between cells.


For those interested in a more exhaustive list with references to phytochemical research, check out the Linus Pauling Institute web page.

While I'm definitely in favor of increasing fruit and vegetable intake for just about everyone, I'm also aware that many individuals have problems tolerating certain foods. Plants in the nightshade family (including tomatoes, eggplant, bell peppers, and potatoes) may be problematic for those with inflammatory conditions such as rheumatoid arthritis. People with irritable bowel syndrome or  other fructose malabsoprtion may benefit from following the FODMAP approach, which limits foods containing Fermentable Oligosaccharides, Disaccharides, Monosaccharides,And Polyols (I plan to blog on this concept at a future date). Others may not feel great after eating certain plant foods or simply not find them appetizing. Obviously, if something doesn't agree with you, you shouldn't eat it no matter how healthy it's purported to be. Fortunately, there are a number of vegetables and fruits that each person can tolerate and enjoy; it may just take some time and experimentation to find them.

I  see great benefit to eating animal protein and fats on a daily basis. But in order to make a low-carb diet a truly healthy way of eating, liberal intake of plant foods is important too. 

References
1.Barzel US, Massey LK: Excess dietary protein can adversely affect bone. J Nutr Jun; 128: 1051-1053, 1988
2. Post, RE, et al. Dietary Fiber for the Treatment of Type 2 Diabetes Mellitus. J Am Board Fam Med Jan-Feb; 25:16-23, 2012 
3.Galland L. Diet and Inflammation. Nutr Clin Pract Dec; 25(6):634-40, 2010