In the video below, Dr. Michael Greger explores the link between obesity and the cancer-causing agent IGF-1* (insulin-like growth factor) produced by fat cells. Children and adults with a higher body mass index (BMI) typically have higher levels of IGF-1. We’ve also summarized his main points below.

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Studies suggest those who eat a vegan diet have lower levels of IGF-1 than meat-eaters and vegetarians. Looking at the chart below, they also have lower BMIs. So can one lower their levels of this cancer-causing hormone just by lowering their BMI?

IGF-1 Levels Average BMI

For answers, Dr. Greger looked at studies that compared long distance runners to plant-based eaters. The runners had similar BMIs to the plant-based eaters, but still ate meat and dairy. Blood tests showed that those eating a low fat, plant-based diet still had lower levels of IGF-1 than long distance runners.

IGF-1 Plasma levels Vegans Runners

Whole plant-foods typically have fewer calories than those included in the Western diet. So could it be that vegans are simply eating fewer calories? When compared with people eating a calorie-restrictive diet, plant-based eaters still had the lowest levels of IGF-1.

IGF-1 Article inset photo 3

While BMI is a factor in cancer risk, IGF-1 is lowest in those who eat a low-fat, whole foods plant-based diet. It is not how many calories, but which calories that seem to determine cancer risk. Watch the video to learn why scientists suggest, “reduced protein intake may become an important component of anticancer and anti-aging dietary interventions.”

*IGF-1: Insulin-like growth factor (IGF-1) is a natural human growth hormone instrumental in normal growth during childhood, but in adulthood can promote abnormal growth—the proliferation, spread (metastasis), and invasion of cancer.

Dr. Greger’s Video Sources:
D L Katz. Facing the facelessness of public health: what’s the public got to do with it? Am J Health Promot. 2011 Jul-Aug;25(6):361-2.
G De Pergola, F Silverstris. Obesity as a major risk factor for cancer. J Obes. 2013;2013:291546.
M Badr, T Hassan, S E Tarhony, W Metwally. Insulin-like growth factor-1 and childhood cancer risk. Oncol Lett. 2010 Nov;1(6):1055-1059.
G K Reeves, K Pirie, V Beral, J Green, E Spencer, D Bull, Million Women Study Collaboration. Cancer incidence and mortality in relation to body mass index in the Million Women Study: cohort study. BMJ. 2007 Dec 1;335(7630):1134.
A G Renehan, M Tyson, M Egger, R F Heller, M Zwahlen. Body-mass index and incidence of cancer: a systematic review and meta-analysis of prospective observational studies. Lancet. 2008 Feb 16;371(9612):569-78.
A G Renehan, M Zwahlen, C Minder, S T O’Dwyer, S M Shalet, M Egger. Insulin-like growth factor (IGF)-I, IGF binding protein-3, and cancer risk: systematic review and meta-regression analysis. Lancet. 2004 Apr 24;363(9418):1346-53.
S C Larsson, A Wolk. Excess body fatness: an important cause of most cancers. Lancet. 2008 Feb 16;371(9612):536-7.
O Shevah, Z Laron. Patients with congenital deficiency of IGF-I seem protected from the development of malignancies: a preliminary report. Growth Horm IGF Res. 2007 Feb;17(1):54-7.
U N Das, When less is adequate: protein and calorie restriction boosts immunity and possibly, longevity–but how and why? Nutrition. 2009 Sep;25(9):892-5.
L Fontana, S Klein, J O Holloszy. Long-term low-protein, low-calorie diet and endurance exercise modulate metabolic factors associated with cancer risk. Am J Clin Nutr. 2006 Dec;84(6):1456-62.
M F McCarty. A low-fat, whole-food vegan diet, as well as other strategies that down-regulate IGF-I activity, may slow the human aging process. Med Hypotheses. 2003 Jun;60(6):784-92.
N E Allen, P N Appleby, G K Davey, R Kasks, S Rinaldi, T J Key. The associations of diet with serum insulin-like growth factor I and its main binding proteins in 292 women meat-eaters, vegetarians, and vegans. Cancer Epidemiol Biomarkers Prev. 2002 Nov;11(11):1441-8.
R L Westley, F E May. A twenty-first century cancer epidemic caused by obesity: the involvement of insulin, diabetes, and insulin-like growth factors. Int J Endocrinol. 2013;2013:632461.
Y Goto, I Sekine, M Tanioka, T Shibata, C Tanai, H Asahina, H Nokihara, N Yomamoto, H Kunitoh, Y Che, H Kikkawa, E Ohki, T Tamura. Figitumumab combined with carboplatin and paclitaxel in treatment-naïve Japanese patients with advanced non-small cell lung cancer. Invest New Drugs. 2012 Aug;30(4):1548-56.
M Honhai, Z Tiehong, S Hongchang, C Honxin, D Jiajun. The adverse events profile of anti-IGF-1R monoclonal antibodies in cancer therapy. British Journal of Clinical Pharmacology. 2014 June;77(6):917–928.
S E Dunn, F W Kari, J French, J R Leininger, G Travlos, R Wilson, J C Barrett. Dietary restriction reduces insulin-like growth factor I levels, which modulates apoptosis, cell proliferation, and tumor progression in p53-deficient mice. Cancer Res. 1997 Nov 1;57(21):4667-72.
L Fontana, E P Weiss, D T Villareal, S Klein, and J O Holloszy. Long-term effects of calorie or protein restriction on serum IGF-1 and IGFBP-3 concentration in humans. Aging Cell. Oct 2008; 7(5): 681–687.
L Fontana, E P Weiss, D T Villareal, S Klein, and J O Holloszy. Long-term effects of calorie or protein restriction on serum IGF-1 and IGFBP-3 concentration in humans. Aging Cell. Oct 2008; 7(5): 681–687.

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