On pages 320-25 of The Hypercarnivore Diet, I recommended fruit be the principle plant food (up to 30% of energy) in a hypercarnivore diet. In that book, I correctly recognized that we have multiple adaptations to fruit consumption (including a taste for sugar and a frugivore-type gut), but I held incorrect beliefs about sugar (especially fructose) that were based on poor quality biased research and low-carbohydrate diet ideology that I had not sufficiently critically evaluated.
Since then I have upgraded my perspective. Fruit is not just a tolerable optional for a healthy hypercarnivore diet; I now think many if not all people can benefit from some amount of fruit in the diet, providing sugar, vitamins and minerals that support gaining and maintaining strength and health.
Fruit consumption supports health by providing sugars, vitamins, minerals, and various phytochemicals that have beneficial properties.
Yes, contrary to popular belief, the sugars that naturally occur in fruits, honey, and tree saps (e.g. maple syrup, birch syrup)–including fructose, sucrose, and others that occur in lesser amounts–are beneficial to health, provided you do not consume so much that you encourage growth of oral bacteria that cause tooth decay. These sugars–particularly fructose in combination with glucose– regulate appetite, enhance thermogenesis, enhance mineral absorption, and counteract stress hormones.
Extreme restriction of carbohydrate intake (such as fasting and ketogenic diets) activates the stress response including an elevation of cortisol and adrenaline, both at rest and in response to exercise.1, 2, 3, 19
Sugar consumption reduces the stress response, which is likely why people crave sugar when under stress.4
Low carbohydrate and ketogenic diets can cause thyroid dysfunction, in part because insulin signaling up-regulates thyroid activity .5, 6, 7, 8
You don't have to eat a "high carbohydrate diet" to prevent these undesired effects. Evidently you can prevent it by eating sufficient excess protein or somewhere between 65 and 180 g of carbohydrate (sugar) daily.30
Of these options, consuming sufficient sugar from milk products and/or fruit may be more desirable for two reasons. First, it reduces the burden on the liver and kidneys for generation of glucose from amino acids and excretion of the nitrogenous waste (urea). Second, eating some sugar from fruit will enhance liver glycogen storage.
Resistance exercise is fueled primarily by the anaerobic glycolytic energy system. This requires glycogen. Fructose is required for normal glucose absorption and metabolism, and consuming fructose+glucose (as in fruit and honey) doubles liver glycogen storage to protect against hypoglycemia.9, 10 , 11
Fructose and sucrose increase metabolic rate and thermogenesis and correct defects in carbohydrate oxidation and thermogenesis found in aging, obesity, and diabetes.12, 13, 14, 15 ,, , Fructose and sucrose produce a higher thermogenic effect (metabolic rate) than starch.16 Fructose and sucrose prevent depression of metabolism when reducing food intake to lose body fat.17
A systematic review of quality research on the impact of whole, fresh fruit consumption on energy intake and body fat levels published in 2019 concluded that evidence from higher quality randomized controlled trials suggests that increasing whole, fresh fruit consumption promotes either weight maintenance or modest weight loss over periods of 3–24 weeks.18 This review also found that single-meal trials suggest that consuming whole, fresh fruit before or during meals tends to decrease energy intake.
Fruits supply vitamins and minerals that are relatively poorly supplied by meats, eggs and dairy products, particularly vitamin C, potassium (as citrate) and boron.
Fruits also have an alkaline residue (bicarbonate) which balances the acid residue of animal products. We have some evidence that eating a more fruit (and therefore potassium citrate) protects against loss of muscle mass with aging.20
Hypercalciuria, urine acidification, and hypocitraturia, all known risk factors for kidney stones, often occur on ketogenic diets, and about 6% of children who use a ketogenic diet to control seizures develop (mostly uric acid) kidney stones as a consequence, but when they supplement with potassium citrate the incidence of stone formation declines 7-fold.31, 32
These data suggest that if you don't include some fruit in your carnivorous diet, it may be wise to use a potassium citrate supplement on a daily basis, especially if you have a personal or family history of uric acid kidney stones.
Phytochemicals in fruit can improve muscle function, block endotoxin absorption, reduce inflammation and enhance intestinal microbiome and metabolism. Here's a few examples of the research:
Apple flavonoids may protect against muscle damage or strain from eccentric contractions.21
Citrus flavonoids reduce both systemic and skin inflammation.22, 23 They block endotoxin absorption and toxicity, protecting against atherosclerosis and diabetes.24, 25, 26
Grape polyphenols (resveratrol, also provided by other plants) also suppress post-meal endotoxin levels, oxidative stress and inflammation.27, 28, 29
As always, each individual must determine his/her tolerance for fruits (or any other food) by personal experiment. For more details, get a copy of Meats & Sweets: A High Vitality Diet. Stay tuned for future publications providing more evidence for the use of fruits for gaining strength and health.
1. Ryan KK, Packard AEB, Larson KR, et al. Dietary Manipulations That Induce Ketosis Activate the HPA Axis in Male Rats and Mice: A Potential Role for Fibroblast Growth Factor-21. Endocrinology. 2018;159(1):400–413. doi:10.1210/en.2017-00486 <https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5761593/>
2. Fraser DD, Whiting MB, Andrew RD, et al. Elevated polyunsaturated fatty acids in blood serum obtained from children on the ketogenic diet. Neurology 2003:60:1026-1029.
3. Anderson KE, Rosner W, Khan MS, et al. Diet-hormone interactions: Protein/carbohydrate ratio alters reciprocally the plasma levels of testosterone and cortisol and their respective binding globulins in man. Life Sciences 1987;40(18):1761-1768.
4. Laugero, K. (2001). A New Perspective on Glucocorticoid Feedback: Relation to Stress, Carbohydrate Feeding and Feeling Better. Journal of Neuroendocrinology 2001:13(9):827-35.
5. Lartey LJ, Werneck-de-Castro JP, O-Sullivan I, Unterman TG, Bianco AC. Coupling between Nutrient Availability and Thyroid Hormone Activation. J Biol Chem. 2015;290(51):30551–30561. doi:10.1074/jbc.M115.665505 <https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4683275/>
6. McCarty, M. (1995). Central insulin may up-regulate thyroid activity by suppressing neuropeptide Y release in the paraventricular nucleus. Medical Hypotheses, 45(2), 193-199.
7. Kose E, Guzel O, Demir K, Arslan N. Changes of thyroid hormonal status in patients receiving ketogenic diet due to intractable epilepsy. J Pediatr Endocrinol Metab 2017 Apr 1;30(4):411-416. Abstract.
8. Kose E, Guzel O, Demir K, Arslan N. Changes of thyroid hormonal status in patients receiving ketogenic diet due to intractable epilepsy. J Pediatr Endocrinol Metab 2017 Apr 1;30(4):411-416. Abstract.
9. Laughlin MR. Normal roles for dietary fructose in carbohydrate metabolism. Nutrients. 2014;6(8):3117–3129. Published 2014 Aug 5. doi:10.3390/nu6083117
10. Gonzalez JT, Fuchs CJ, Betts JA, et al. Glucose Plus Fructose Ingestion for Post-Exercise Recovery–Greater than the Sum of Its Parts? Nutrients 2017 Apr;9(4):344. doi: 10.3390/nu9040344.
11. Sun SZ, Empie MW. Fructose metabolism in humans - what isotopic tracer studies tell us. Nutr Metab (Lond). 2012;9(1):89. Published 2012 Oct 2. doi:10.1186/1743-7075-9-89 <https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3533803/>
12. Schwarz JM, Schutz Y, Froidevaux F, Acheson KJ, Jeanprêtre N, Schneider H, Felber JP, Jéquier E. Thermogenesis in men and women induced by fructose vs glucose added to a meal. Am J Clin Nutr. 1989 Apr;49(4):667-74. PubMed PMID:2648796.
13. Tappy L, Randin JP, Felber JP, Chiolero R, Simonson DC, Jequier E, DeFronzo RA. Comparison of thermogenic effect of fructose and glucose in normal humans. Am J Physiol. 1986 Jun;250(6 Pt 1):E718-24. PubMed PMID: 3521319.
14. Tappy L, Jéquier E. Fructose and dietary thermogenesis. Am J Clin Nutr. 1993 Nov;58(5 Suppl):766S-770S. doi: 10.1093/ajcn/58.5.766S. Review. PubMed PMID: 8213608.
15. Simonson DC, Tappy L, Jequier E, Felber JP, DeFronzo RA. Normalization of carbohydrate-induced thermogenesis by fructose in insulin-resistant states. Am J Physiol. 1988 Feb;254(2 Pt 1):E201-7. PubMed PMID: 3279802.
16. Blaak EE, Saris WH. Postprandial thermogenesis and substrate utilization after ingestion of different dietary carbohydrates. Metabolism. 1996 Oct;45(10):1235-42. PubMed PMID: 8843178.
17. Hendler RG, Walesky M, Sherwin RS. Sucrose substitution in prevention and reversal of the fall in metabolic rate accompanying hypocaloric diets. Am J Med. 1986 Aug;81(2):280-4. PubMed PMID: 3740086.
18. Guyenet SJ. Impact of Whole, Fresh Fruit Consumption on Energy Intake and Adiposity: A Systematic Review. Front Nutr. 2019;6:66. Published 2019 May 8. doi:10.3389/fnut.2019.00066 <https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6518666/>
19. Langfort J, Pilis W, Zarzeczny R, Nazar K, Kaciuba-Uściłko H. Effect of low-carbohydrate-ketogenic diet on metabolic and hormonal responses to graded exercise in men. J Physiol Pharmacol. 1996 Jun;47(2):361-71. PubMed PMID: 8807563.<https://www.ncbi.nlm.nih.gov/pubmed/8807563> “Both the pre-and post-exercise levels of adrenaline, noradrenaline, and cortisol were enhanced, whilst plasma insulin concentration was decreased on the ketogenic diet. “
20. Dawson-Hughes B, Harris SS, Ceglia L. Alkaline diets favor lean tissue mass in older adults. Am J Clin Nutr. 2008;87(3):662–665. doi:10.1093/ajcn/87.3.662 <https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2597402/>
21. Nakazato, K., Ochi, E., & Waga, T. (2010). Dietary apple polyphenols have preventive effects against lengthening contraction‐induced muscle injuries. Molecular Nutrition & Food Research, 54(3), 364-372.
22. Lorzadeh, E., Ramezani-Jolfaie, N., Mohammadi, M., Khoshbakht, Y., & Salehi-Abargouei, A. (2019). The effect of hesperidin supplementation on inflammatory markers in human adults: A systematic review and meta-analysis of randomized controlled clinical trials. Chemico-Biological Interactions, 307, 8-15.
23. Man MQ, Yang B, Elias PM. Benefits of Hesperidin for Cutaneous Functions. Evid Based Complement Alternat Med. 2019;2019:2676307. Published 2019 Apr 2. doi:10.1155/2019/2676307
24. Deopurkar R, Ghanim H, Friedman J, et al. Differential effects of cream, glucose, and orange juice on inflammation, endotoxin, and the expression of Toll-like receptor-4 and suppressor of cytokine signaling-3. Diabetes Care. 2010;33(5):991–997. doi:10.2337/dc09-1630
25. Rotimi SO, Bankole GE, Adelani IB, Rotimi OA. Hesperidin prevents lipopolysaccharide-induced endotoxicity in rats. Immunopharmacol Immunotoxicol. 2016 Oct;38(5):364-71. doi: 10.1080/08923973.2016.1214142. Epub 2016 Aug 2. PubMed PMID: 27427274.
26. Ghanim H, Sia CL, Upadhyay M, et al. Orange juice neutralizes the proinflammatory effect of a high-fat, high-carbohydrate meal and prevents endotoxin increase and Toll-like receptor expression [published correction appears in Am J Clin Nutr. 2011 Mar;93(3):674. Upadhyay, Mannish [corrected to Upadhyay, Manish]]. Am J Clin Nutr. 2010;91(4):940–949. doi:10.3945/ajcn.2009.28584
27. Ghanim H, Sia CL, Korzeniewski K, et al. A resveratrol and polyphenol preparation suppresses oxidative and inflammatory stress response to a high-fat, high-carbohydrate meal. J Clin Endocrinol Metab. 2011;96(5):1409–1414. doi:10.1210/jc.2010-1812
28. Leifert WR, Abeywardena MY. Cardioprotective actions of grape polyphenols. Nutr Res. 2008 Nov;28(11):729-37. doi: 10.1016/j.nutres.2008.08.007. Review. PubMed PMID: 19083481.
29. Singh CK, Liu X, Ahmad N. Resveratrol, in its natural combination in whole grape, for health promotion and disease management. Ann N Y Acad Sci. 2015;1348(1):150–160. doi:10.1111/nyas.12798
30. Wolfe, R.R.A.K.S. (1992). Carbohydrate restriction regulates the adaptive response to fasting. AJP - Endocrinology and Metabolism, 262, E631
31. Furth SL, Casey JC, Pyzik PL, et al.. Risk factors for urolithiasis in children on the ketogenic diet. Pediatr Nephrol. 2000 Nov;15(1-2):125-8. PubMed PMID: 11095028.
32. McNally MA, Pyzik PL, Rubenstein JE, Hamdy RF, Kossoff EH. Empiric use of potassium citrate reduces kidney-stone incidence with the ketogenic diet. Pediatrics. 2009;124(2):e300–e304. doi:10.1542/peds.2009-0217
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