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Table 1.

Summary of the evidence for associations between dietary factors and serum IGF-I

Nutrient/food groupStudies using animal models*Cross-sectional studies in humansExperimental studies in humans*Conclusion
Energy Severe energy restriction results in 25% decreased serum IGF-I (review; ref. 75) No association (8×; refs. 68, 63, 69, 71, 66, 72, 73, 74) Serum IGF-I is markedly lowered by energy deprivation (review; ref. 60) Probable; positive association with extremes of energy intake 
  Positive association (2×; refs. 67, 70)  No association within normal range of energy intake 
Protein (total or animal) Severe protein restriction results in 50% decreased serum IGF-I (review; ref. 61) No association with total and/or animal protein (6×; refs. 64, 66, 71, 73, 74) Serum IGF-I is markedly lowered by protein deprivation (review; ref. 60) Possible; positive association with intake of animal protein 
  Positive association with total or animal protein (5×; refs. 63, 67, 68, 69, 70)   
Alcohol Chronic alcohol feeding may increase or decrease serum IGF-I No association with IGF-I (5×; refs. 64, 67, 68, 72, 74) Decline in serum IGF-I after drinking alcohol (1 d only) No association within normal range of alcohol consumption 
  Minor inverse association (66)   
  Positive association (in men only; ref. 62  
Minerals (total or zinc) Mineral (e.g., zinc, copper, and magnesium) deficiency is associated with low serum IGF-I levels No association with zinc (68) Zinc supplementation: increased serum IGF-I levels in specific populations (anemic, non-insulin-dependent diabetes mellitus) Probable; positive association with zinc or a combination of minerals (including supplements) 
  Positive association with zinc (63, 67)   
  Positive association with combined intake of five minerals (including zinc; ref. 69  
Dairy products Only studies relating to IGF-I content in milk (review; ref. 79) No association with total dairy (64, 66, 68, 71; one positive association with milk only; ref. 71) Serum IGF-I increased 10% with three servings of dairy daily (77) Possible; positive association with consumption of dairy/milk 
  Positive association with total dairy (67  
  Positive association with milk (65, 69)   
Soy or isoflavones Decrease in serum IGF-I in animals on soy protein/phytoestrogen diet (93, 94) Asian populations: no association with soy or isoflavones (72); positive association (in men only; ref. 73Soy protein vs. milk protein: stronger increase in IGF-I in soy protein group (99, 100) Insufficient; association could be positive or inverse, depending on dose and population 
  European population (including vegans/vegetarians): no association with soy protein (borderline positive with soy milk; ref. 68) Soy protein with vs. without isoflavones: trend towards lower IGF-I with isoflavones (postmenopausal women only; ref. 98) or no difference between groups (101) Effects of soy protein and isoflavones/phytoestrogens to need be disentangled (possibly opposite effects) 
  European population (low intake): no association with soy or isoflavones (74)   
Tomatoes or lycopene Increased plasma IGFBP-3 concentration in ferrets receiving lycopene (8) Tomato products: no association (64, 71, 74; 1× inverse with IGF-I/IGFBP-3 ratio; ref. 71); inverse association (66) Lycopene intervention: IGF-I decreased in both intervention and control groups (85) Insufficient; inverse association with IGF (or IGF/IGFBP-3 ratio); positive association with IGFBP-3 
  Lycopene intake: no association (positive with IGFBP-3; ref. 67  
Nutrient/food groupStudies using animal models*Cross-sectional studies in humansExperimental studies in humans*Conclusion
Energy Severe energy restriction results in 25% decreased serum IGF-I (review; ref. 75) No association (8×; refs. 68, 63, 69, 71, 66, 72, 73, 74) Serum IGF-I is markedly lowered by energy deprivation (review; ref. 60) Probable; positive association with extremes of energy intake 
  Positive association (2×; refs. 67, 70)  No association within normal range of energy intake 
Protein (total or animal) Severe protein restriction results in 50% decreased serum IGF-I (review; ref. 61) No association with total and/or animal protein (6×; refs. 64, 66, 71, 73, 74) Serum IGF-I is markedly lowered by protein deprivation (review; ref. 60) Possible; positive association with intake of animal protein 
  Positive association with total or animal protein (5×; refs. 63, 67, 68, 69, 70)   
Alcohol Chronic alcohol feeding may increase or decrease serum IGF-I No association with IGF-I (5×; refs. 64, 67, 68, 72, 74) Decline in serum IGF-I after drinking alcohol (1 d only) No association within normal range of alcohol consumption 
  Minor inverse association (66)   
  Positive association (in men only; ref. 62  
Minerals (total or zinc) Mineral (e.g., zinc, copper, and magnesium) deficiency is associated with low serum IGF-I levels No association with zinc (68) Zinc supplementation: increased serum IGF-I levels in specific populations (anemic, non-insulin-dependent diabetes mellitus) Probable; positive association with zinc or a combination of minerals (including supplements) 
  Positive association with zinc (63, 67)   
  Positive association with combined intake of five minerals (including zinc; ref. 69  
Dairy products Only studies relating to IGF-I content in milk (review; ref. 79) No association with total dairy (64, 66, 68, 71; one positive association with milk only; ref. 71) Serum IGF-I increased 10% with three servings of dairy daily (77) Possible; positive association with consumption of dairy/milk 
  Positive association with total dairy (67  
  Positive association with milk (65, 69)   
Soy or isoflavones Decrease in serum IGF-I in animals on soy protein/phytoestrogen diet (93, 94) Asian populations: no association with soy or isoflavones (72); positive association (in men only; ref. 73Soy protein vs. milk protein: stronger increase in IGF-I in soy protein group (99, 100) Insufficient; association could be positive or inverse, depending on dose and population 
  European population (including vegans/vegetarians): no association with soy protein (borderline positive with soy milk; ref. 68) Soy protein with vs. without isoflavones: trend towards lower IGF-I with isoflavones (postmenopausal women only; ref. 98) or no difference between groups (101) Effects of soy protein and isoflavones/phytoestrogens to need be disentangled (possibly opposite effects) 
  European population (low intake): no association with soy or isoflavones (74)   
Tomatoes or lycopene Increased plasma IGFBP-3 concentration in ferrets receiving lycopene (8) Tomato products: no association (64, 71, 74; 1× inverse with IGF-I/IGFBP-3 ratio; ref. 71); inverse association (66) Lycopene intervention: IGF-I decreased in both intervention and control groups (85) Insufficient; inverse association with IGF (or IGF/IGFBP-3 ratio); positive association with IGFBP-3 
  Lycopene intake: no association (positive with IGFBP-3; ref. 67  

NOTE: “Probable”: The association (or lack of) is consistently shown in cross-sectional studies and confirmed by experimental studies in animals and in humans. “Possible”: Association in some but not all cross-sectional studies; experimental studies in animals consistently show the association; however, no or only one experimental study in humans is available. “Insufficient”: Only very few studies have been conducted and these are not entirely consistent.

*

References are only included if a review article is available or if literature is limited to one or two studies.

All published cross-sectional studies (n = 13) are included; references of studies including >500 individuals are printed in bold.

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