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Dr. Sears' Blog

Keep Up with the Latest Nutrition Science
Written By: Dr. Barry Sears Creator of the Zone Diet

Written by Dr. Barry Sears
on March 03, 2021

Since February was heart month, I thought it worthwhile to discuss the relationship between milk and heart health. Dairy milk consumption in the US has decreased by 40% since 1975, but total dairy consumption (milk, cheese, yogurt, and butter) has never been higher. As an example, cheese consumption is up by about 160% since 1975. Furthermore, while dairy milk consumption is decreasing, plant-based “milk” consumption is increasing. It started with soy milk (too beany), then coconut and almond milk (deficient in protein), followed by rice, oat, hemp, and more increasingly exotic plant-based “milk” products. Why? It beats me. Dairy milk is probably the most inexpensive, high-quality protein source (only egg whites have a higher protein quality). Milk also contains calcium, magnesium and potassium, and Vitamin D. So, what’s the problem?

A recent study in the British Journal of Nutrition may help explain the controversy (1). The largest consumers of dairy products in the world are the Finnish. When they analyzed collected data over a nearly 30 year period and then made all the appropriate adjustments to the raw data, they found that fermented and non-fermented dairy products had opposite associations with the risk of developing heart disease. Those consuming fermented dairy products had a 26 percent lower risk of Coronary Heart Disease (CHD), and those consuming non-fermented dairy products had a 43 percent greater risk of CHD. Furthermore, in the fermented dairy group, the lower the fat content (less than 3.5 percent fat), the less CHD they developed.

When you ferment dairy products, you are removing lactose. Dairy milk is about 5 percent lactose. To make yogurt, you add bacterial cultures that break some of the lactose into glucose and galactose. The amount of lactose in yogurt is about 4 percent. When you make cheese, the process is more complicated. First, you start by adding a bacterial culture to pasteurized milk to reduce the initial lactose levels. Then you add rennet, a combination of proteases and lipases. Rennet is the dried inner lining of the fourth stomach chamber of young calves (a byproduct of veal production) to curdle the milk's casein protein. This natural form of rennet is the preferred choice for high-quality cheeses. For more mass-produced cheeses, they use enzymes derived from molds. Whatever the source of rennet, the addition of rennet makes curds leaving much of the lactose and whey protein in the solution. The milk curds are collected and then aged to either make soft cheeses (about 2% lactose) or hard cheeses (about 1% lactose).

Okay, but what about the reports of associations of dairy milk consumption and increased IGF-1 levels? IGF-1 is a growth factor that might be associated with breast cancer (2). A recent observational study suggested a potential linkage between IGF-1 and breast cancer (3). However, an earlier study suggested the opposite conclusions (4). The controversy may be related to the fact that non-fermented dairy products increase IGF-1, whereas fermented dairy products don’t increase IGF-1 levels (5). Reducing cancer risk using fermented dairy products is also suggested by a recent meta-analysis (6).

In this era of conflicting claims of dairy products and chronic disease, it seems your best bet is to remove as much of the lactose from dairy products that you possibly can and still retain all of the nutritional benefits found in dairy products. The best high-tech way is to make completely lactose-free milk by treating the dairy milk with the enzyme that breakdowns down the lactose into glucose and galactose. Now you have entirely lactose-free dairy milk with all the benefits of inexpensive, high-quality proteins and associated vitamins and minerals. This elimination of lactose is why all of our products either use lactose-free dairy protein or recommend using lactose-free milk in our ZoneRx shakes. To paraphrase Neville Chamberlain, it brings dietary “peace in our time” as well as better health.

Let us know your stance on dairy in the comments below.


1. Koskinen TT et al. Intake of fermented and non-fermented dairy products and the risk of incident CHD. Brit J Nutr 120:1288-1297 (2018)

2. Monson KR et al. Circulating growth factor concentrations and breast cancer risk: a nested case-control study of IGF-1, IGFBP-3, and breast cancer in a family-based cohort. Breast Cancer Res 22:109 (2020).

3. Fraser GE et al. Dairy, soy, and risk of breast cancer. Int J Epidemiology 49: 1526–1537 (2020)

4. Hjartaker A et al. Childhood and adult milk consumption and risk of premenopausal breast cancer in a cohort of 48,844 women - the Norwegian women and cancer study. Int J Cancer 93: 888–893 (2001)

5. Ventura ER et al. Association of dietary intake of milk and dairy products with blood concentrations of insulin-like growth factor 1 (IGF-1) in Bavarian adults. Eur J Nutr

59:1413-1420 (2020)

6. Zhang K et al. Fermented dairy foods intake and risk of cancer. Int J Cancer 144:2099-2108 (2019)

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