There's little scientific evidence behind recommendations by US health organizations that kids should stop eating full-fat dairy after the age of two, according a new analysis of 29 peer-reviewed studies on the role of dairy and childhood obesity.
'Taken as a whole, the limited literature in this field is not consistent with dietary guidelines recommending children consume preferably reduced-fat dairy products,' said lead author Therese O'Sullivan, a clinical dietitian at Edith Cowan University in Australia.
Current guidelines (PDF) from the American Heart Association, the American Academy of Pediatrics and other major US organizations only recommend whole milk and dairy for children aged 12 to 24 months. Australia (PDF) and the UK have similar guidelines.
Diary is an important source of calcium and fat for children, and also provides important nutrients such as protein, iodine, riboflavin and Vitamin B12.
If the child is growing well, existing guidelines suggest parents switch to low-fat dairy products starting at age two to protect children from the risk of obesity and cardiovascular disease. The UK does not recommend skim milk for children under five.
Cardiovascular disease is the number one killer of adults worldwide. Last year, a study by the World Obesity Organization predicted that the number of obese children around the world will grow from 150 million currently to 250 million by 2030.
Whole or low-fat?
The new study, published Monday in the journal Advances in Nutrition, found whole-fat dairy products were not linked to weight gain, obesity or any measures of cardiovascular disease risk.
A similar analysis published in December found children drinking whole-fat cow's milk were less likely to be obese than those who drank the low-fat version, although researchers couldn't show a cause and effect.
The American Academy of Pediatrics' Committee on Nutrition 'reviewed the literature and came up with very similar results,' said pediatric endocrinologist Dr. Tamara Hannon, a member of the AAP committee. She was not involved in any of the studies.
'You can't come to the conclusion that eating full fat dairy is associated with either excessive weight gain or increased cardiovascular risk factors because that's just not what these studies find,' said Hannon, who directs the Pediatric Diabetes Program at Riley Hospital for Children in Indianapolis, Indiana.
But that doesn't mean that recommendations will be immediately changed or that parents should start giving their child full-fat dairy. Why not? Because of the quality of the research that's been done on the topic.
For example, research may be supported by grants from the dairy industry. While that doesn't necessarily negate the findings, the optics aren't good. Many of the studies are 'observational' studies, which is a type of research that can only find an association between two outcomes; it cannot establish cause and effect. Randomized controlled trials -- the gold standard of science -- are expensive and difficult to do in nutrition.
In the current review, for example, only two of the studies were more scientifically based, yet even those results were questionable. In one, researchers asked children in Mexico to switch from full to low-fat dairy and found there was no difference in their weight at the end of the study.
'But that was because they were eating more tortillas along with the reduced-fat milk, so they were getting the same numbers of calories,' Hannon explained.
On the other hand, 'whole fat milk may lead to higher satiety, and therefore smaller portions and similar calorie intake,' said Stanford professor of medicine Christopher Gardner, who directs nutrition studies at Stanford Prevention Research Center.
'I think the bigger questions are: Are either of them -- whole or reduced fat -- 'good' for you? And what you [or your child] would be drinking instead of milk?' said Gardner, who was not associated with the study. 'If it's milk versus soda, I would pick milk. If it's milk versus water, I'd pick water.'
What to do?
Definitive answers to the role of milk -- whole or not -- for both adults and children need additional research, experts say.
A recent review by Harvard nutritionists Dr. Walter Willett and Dr. David Ludwig, published in the New England Journal of Medicine, looked at the role of milk in bone health, cancer, weight gain and cardiovascular risk.
'Overall, the findings of prospective cohort studies and randomized trials do not show clear effects of milk intake on body weight in children or adults,' the review concludes.
Of course there would be benefits in countries where malnutrition is an issue, so the overall quality of a child's diet is key in making recommendations.
For adults, there are negative associations between milk and health. The review points out that despite the fact that milk is recommended for 'strong bones,' countries with the highest intakes of milk and calcium have the highest rates of hip fractures. Studies also show no clear benefit of calcium in reducing bone fractures.
In regards to cancer, the review found high consumption of dairy foods was associated with an increased risk of prostate cancer and may contribute to endometrial cancer. But it appears to reduce the risk of colorectal cancer.
'The health benefit of a high intake of milk products has not been established, and concerns exist about the risks of possible adverse health outcomes,' Willett and Ludwig wrote. 'Therefore, the role of dairy consumption in human nutrition and disease prevention warrants careful assessment.'
The 2020-2025 nutritional guidelines for adults and children in the US will be released soon. Until then, Hannon suggests parents discuss their individual family risk with their health care provider to decide on the role of dairy in their family's diet -- whole or not.
'If you have a very strong family history of cardiovascular disease with heart attacks and things like that, you would want to choose a different dietary path and avoid full-fat dairy more than a family without those risk factors,' Hannon said.