The idea that calorie intake alone determines successful weight control is losing ground.

However, debates over the best mix of food types for weight control continue to rage.

So far, the evidence doesn't strongly favor either low-fat or low-carb diets.

But the comparative studies rarely account for the specific types and sources of fats and carbs being consumed.
So it's still unclear whether Paleo-type diets (high-protein/moderate-fat/low-carb) or Ornish-type diets (low-fat/high-carb/plant-based) are best for weight control. 

However, it's become increasingly apparent that the two types of polyunsaturated fat essential to human health – omega-6 and omega-3 – exert opposing effects on weight gain.

The average American's diet has a severe "Omega imbalance" – far too many omega-6 fats from vegetable oils, and too few omega-3s from seafood.

Persuasive (if not conclusive) evidence now links that imbalance to increased risks for heart disease, metabolic syndrome, diabetes, and dementia, among other chronic health problems.

And animal studies show that diets weighted too heavily toward omega-6 intake promote weight gain: see Omega-6 Fats Drive Obesity; Omega-3s Help and Excess Omega-6 Fat Intakes Promote Weight Gain.

Growing evidence of the dangers of America's omega imbalance led the U.S. National Institutes of Health to issue this advisory: "There is general agreement that individuals should consume more omega-3 and less omega-6 fatty acids to promote good health."

Given America's struggle with obesity, it seems urgent to discover whether children's risk for obesity is influenced by the fats they eat ... and/or the fats their mothers eat during pregnancy and nursing.

Children's risk for obesity, and the "Omega balance”
Adiposity – the medical term for excess belly fat – nearly doubled from 1976 to 1994, among six to 11-month old infants in the U.S.   

This sharp rise occurred during the same time span when the omega-6 fat content of infant foods, including breast milk and infant formula, also increased (Alvheim A et al. 2010).

In contrast, infants' intake of omega-3s declined during this period. Associations like these do not establish cause-effect relationships, but raise concerns.

Four years ago, researchers reported that they detected the obesity-promoting effect of America's omega-intake imbalance in children.

For that study, researchers from Harvard Medical School recorded the fat intakes and blood fat profiles of expectant mothers (Donahue SM et al. 2011).

Three years later, they examined the participating women's offspring for two key signs of increased risk for future obesity: higher levels of fat under the skin, and higher body mass indices.

The Harvard team came to two important conclusions:
  • Children born to mothers who consumed more omega-3s were less likely to show warning signs of future obesity.
  • The risk of obesity was higher among the children of mothers whose umbilical cord blood contained high ratios of omega-6 to omega-3 fatty acids. 
University study links children's omega-3 intake to reduced risk for obesity 
A new study from the University of Colorado and the University of Alabama suggests that children who take in more omega-3s than average are less likely to become overweight.

Specifically, the results show that children who ate more omega-3s than their peers had more lean body mass, lower percentages of body fat, and less belly fat (Cardel M et al. 2015).

The Colorado/Alabama team examined a group of racially diverse children aged 7 to 12 years.

Lead author Michelle Cardel, PhD, RD, explained what prompted their new research: "Studies have identified a variety of benefits of including polyunsaturated fatty acids (PUFAs) into an adult's diet, particularly omega-3 fatty acids.” (UCAWC 2015)

Each child provided two separate self-reports of their 24-hour dietary intakes, with parental supervision to help ensure accuracy.

As Dr. Cardel said, "Our data suggests that [higher] consumption of PUFAs is associated with improved body composition in diverse groups of children.” (UCAWC 2015)

Their finding also applied to children who consumed higher ratios of both types of PUFAs – omega-3 and omega-6 – to saturated fats.

But the available evidence suggests that it is far healthier to substitute omega-3s for saturated fats, rather than omega-6s.

"Hopefully this work will stimulate additional research to determine if there is a causal relationship between dietary PUFAs, body fat and lean mass in kids,” Cardel said. "Until then, children should consume fatty fish, such as salmon, twice a week to reach Institute of Medicine recommendations for omega-3 fatty acids.”

Her recommendation also fits with the 2010 official U.S. guidelines – see Eating More Fish Advised in U.S. Diet Guidelines – which will likely be repeated in the upcoming 2015 version.

Note: The "long-chain” omega-3s that the human body actually needs and uses (DHA and EPA) are found only in seafood.

A much less effective "short-chain” form called ALA is found in dark leafy greens, walnuts, chia seeds, and flax seeds.

But most of the omega-3 ALA we eat is burned as fuel ... or, when a person's diet lacks seafood, the body converts very small percentages (one to 10) of dietary ALA into omega-3 DHA.

  • Cardel M, Lemas DJ, Jackson KH, Friedman JE, Fernández JR. Higher Intake of PUFAs Is Associated with Lower Total and Visceral Adiposity and Higher Lean Mass in a Racially Diverse Sample of Children. J Nutr. 2015 Aug 12. pii: jn212365. [Epub ahead of print] 
  • Donahue SM, Rifas-Shiman SL, Gold DR, Jouni ZE, Gillman MW, Oken E. Prenatal fatty acid status and child adiposity at age 3 y: results from a US pregnancy cohort. Am J Clin Nutr. 2011 Apr;93(4):780-8. doi: 10.3945/ajcn.110.005801. Epub 2011 Feb 10.
  • Lund AS, Hasselbalch AL, Gamborg M, Skogstrand K, Hougaard DM, Heitmann BL, Kyvik KO, Sørensen TI, Jess T. N-3 polyunsaturated fatty acids, body fat and inflammation. Obes Facts. 2013;6(4):369-79. doi: 10.1159/000354663. Epub 2013 Aug 16. 
  • University of Colorado Anschutz Health and Wellness Center. (UCAWC) Children who are leaner report eating more polyunsaturated fatty acids. August 12, 2015. Accessed at