Among the various dietary choices available, milk—whether whole, skim, low-fat, organic, or plant-based—remains a staple in many diets. For those concerned with weight management or cardiovascular health, the decision between whole milk and skim milk often raises questions. A recent study published in iMeta provides valuable insights.
In the 21st century, maintaining a good physique, working out, and focusing on nutrition have become integral parts of many people's lives. As material wealth increases, the choices we face also become more diverse, with "milk" being a prime example. Walking into the dairy section of a supermarket, you are greeted by a vast array of milk products: whole milk, skim milk, low-fat milk, organic milk, plant-based milk...
It is widely known that milk is a nutrient-rich drink, often referred to as "the most perfect food," as it contains numerous essential nutrients for human health. However, for many people who are looking to lose weight, stay fit, or manage conditions like high blood pressure, high blood sugar, or high cholesterol, there is a dilemma: should they choose whole milk or skim milk?
Undoubtedly, whole milk is richer in taste and has a stronger milk flavor, while skim milk has lower calories and cholesterol, making it a better option for weight loss and reducing the burden on the body. But which one is really better? The internet is flooded with various suggestions and viewpoints, making it hard to decide. So, is there scientific research that can help us make a more informed decision?
The answer is yes! A recent study published in the iMeta journal delves into the long-term effects of consuming milk fat on serum lipid levels and reveals some unexpected findings. The study shows that drinking whole milk over the long term does not significantly increase lipid levels in the blood. In fact, it may even promote overall health by improving the gut microbiome.
Research Approach and Experimental Design
Traditionally, foods rich in saturated fatty acids (SFAs) have been thought to increase the risk of cardiovascular diseases, and therefore, "whole milk" has been regarded as a potential contributor to obesity and cardiovascular issues. However, recent studies have increasingly suggested that the fats in dairy products may contain components beneficial to human health, such as monounsaturated fatty acids, polyunsaturated fatty acids, omega-3 fatty acids, and medium-chain saturated fatty acids. Additionally, a multinational cohort study has linked dairy consumption to lower mortality rates and reduced risks of major cardiovascular events.
Against this backdrop, the goal of this study was to evaluate whether long-term consumption of milk fat would have a significant impact on the serum lipid levels of mice fed with either a normal diet or a high-fat diet, and to explore the changes in the gut microbiome and metabolic products involved.
To achieve this, the scientists selected a group of male C57BL/6J mice for the study. The mice were divided into two groups: one group was fed a normal standard diet (ND), and the other group received a high-fat diet (HFD).
Before the experiment began, all the mice adapted to the standard diet for one week. Then, they embarked on a 10-week "food challenge." During this period, the mice in the ND and HFD groups were given different dietary treatments. After 10 weeks, each group was further subdivided into six subgroups to receive various types of interventions:
- ND Control Group (N-Ctl): Continued on the standard diet.
- ND Whole Milk Group (N-Mlk): Received additional whole milk daily.
- ND Milk Fat Group (N-Fat): Only consumed the fat portion of the milk.
- HFD Control Group (H-Ctl): Continued on the high-fat diet.
- HFD Whole Milk Group (H-Mlk): Received whole milk in addition to the high-fat diet.
- HFD Milk Fat Group (H-Fat): Received only milk fat in addition to the high-fat diet.
Figure 1: Experimental process
The intervention lasted for 7 weeks, during which the researchers closely monitored the mice’s weight changes, serum lipid levels (such as LDL-C and HDL-C), fat tissue weight, gut microbiome composition, and metabolites in their feces.
Whole Milk Wins by a Small Margin!
After a series of meticulous observations and analyses, the research team arrived at several surprising conclusions:
1. No Significant Weight Gain:
Whether on the ND or HFD, long-term consumption of whole milk or milk fat did not result in significant weight gain in the mice. This suggests that drinking whole milk won't turn you into a "milk fattened" person!
Figure 2: The intake of dairy fat and whole milk did not increase the body weight of mice in the ND or HFD groups, but significantly increased the HDL-C level
2. Healthier Blood Lipids:
The researchers found that milk fat significantly reduced triglyceride levels in the ND mice, meaning their blood became "clearer." Whey protein not only reduced triglycerides in the ND mice but also helped reduce these harmful substances in the HFD mice. Additionally, both milk fat and whole milk increased the levels of beneficial HDL-C in the mice, thereby lowering their risk of atherosclerotic cardiovascular diseases.
3. Improved Gut Microbiome:
Long-term consumption of milk fat increased the diversity of gut microbiota in the ND mice, particularly the strains that help regulate blood lipids, such as Blautia, Akkermansia, and Bacteroides, which showed a significant increase.
Figure 3: Effects of long-term dairy fat and whole milk intake on the composition of the gut microbiota in ND and HFD mice
4. Changes in Metabolic Products:
Through untargeted metabolomics analysis, the researchers identified multiple metabolic products influenced by milk fat, which are involved in pathways such as taurine and low taurine metabolism, as well as steroid hormone biosynthesis. This indicates that milk fat not only affected the gut microbiome but also altered several metabolic pathways in the body.
Figure 4: Different intestinal metabolites and lipid levels in ND and HFD mice after whole milk and milk fat intervention
Summary
To sum up, this research suggests that drinking whole milk or consuming milk fat over the long term doesn’t significantly raise the serum lipid levels in the body. In fact, it may contribute to improving the gut microbiome, boosting the growth of beneficial bacteria, and helping to maintain a healthy balance of blood lipids by influencing certain metabolic pathways. This challenges our previous views on saturated fats and delivers good news for those who enjoy whole milk—allowing them to savor it without worrying too much about health risks.
However, this doesn’t mean we should binge on cheese or indulge in creamy coffee without limits. Moderation is still key, and a well-rounded diet is essential to maintaining healthy lifestyle habits. Moreover, the study highlights that when evaluating the effects of food on our health, we should not focus solely on individual ingredients. It’s important to consider the whole ecosystem, including the trillions of bacteria in our gut—the gut microbiome. Future studies may uncover more insights into how dairy and other foods interact, helping to develop more balanced and evidence-based dietary guidelines.
