Does lactose inhibit fat loss?
In Tim Ferriss' The Four Hour Body, the claim is made that lactose intake seems to inhibit fat loss. Note that it is not claimed that it causes fat gain. Like many claims in this book, it is (and the author is upfront about this) anecdotal and he does not provide an explanation for why it might be so.
So my question: can anyone verify that this is or isn't the case?
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Tim cites this study: www.ajcn.org/content/74/1/96.full, which basically concludes that while milk products have a low glycemic index, they have a high insulinemic index, meaning they cause insulin concentrations to be higher in the blood.
Regarding the study cited by Andrew Ferk, I'm curious about the experiment design, especially the fact that the control group is being fed corn starch, and the experimental group is getting lactose.
It's of concern that the testing isolates lactose instead of feeding the rats milk products, which would include fats and proteins. It's also of concern that the protein:fats:carbs ratios are very low in protein, either 11 or 13 percent.
I think this all adds up to Tim's main point, which is this book is a record of a number of experiments he undertook on himself, and if you aren't approaching it the same way, you might not have good results.
So, maintain a steady diet, and try a month without milk, and a month with, keeping the other balances the same, and see how it affects things.
According to the 2007 study, Effects of Dietary Lactose on Long-term High-fat-diet-induced Obesity in Rats, "the addition of lactose to a high-fat diet decreased body weight, body weight gain, fat accumulation, and the level of serum leptin."
In the study, four groups were observed over 84 days: A control diet group (Cont), a lactose diet group (Lac) in which corn starch in the control diet was replaced by lactose at 10% of the diet weight, a high-fat diet group (Fat) in which lard was added to the control diet to adjust the lipid energy ratio to 40% , and a lactose-added high-fat diet group (Fat+Lac) in which 10% lactose was added to the high-fat diet. The graphs below compares the weight of fats and the amount of serum leptin (a hormone that regulates long-term appetite) between the four groups at the end of the observation.
The graphs show there is no significant difference between the fat accumulation and serum leptin levels between the Cont and Lac group, but the Fat+Lac group does have decreased fat accumulation and serum leptin from the Fat group.
Lactose is broken down by the lactase enzyme into galactose and glucose1. Glucose, of course, stimulates insulin production2, which stimulates fat retention3. So yes, lactose should inhibit fat loss. (Edit) But, as per my comment on Andrew's answer, galactose has the opposite effect as glucose4. I am inclined to believe, due to the results of the study posted in his answer5, that the galactose actually outweighs the glucose and thus lactose actually aids fat loss (at least at <10% energy intake from lactose).
(1): Wikipedia - Lactase
(2): Wikipedia - Insulin
(3): UNU.edu - "The inhibitory effect of insulin on lipolysis in adipose tissue, and the subsequent decline in plasma free fatty acid levels leads to the postprandial inhibition of fat oxidation."
(4): American Journal of Clinical Nutrition
(5): Nature
This is an interesting question, as "Dairy Products" will help you lose weight due to their high calcium concentration (Source). "Lactose" specifically, though, is where the carbohydrates in milk come from, and complex carbohydrates are converted into glycogen in the liver and used for the body's energy source, thus inhibiting the body from burning it's fat as a resource.
Lactose is a disaccharide derived from the condensation of galactose and glucose - Wikipedia
Intake of excessive carbohydrates leads to an uptake in the body's blood sugar levels, triggering the body to produce more insulin. Insulin promotes and aids in fat storage in the body.
In summary, "Milk" and "Dairy Products" in moderation aren't going to have a major effect on your fat loss, but excessive amounts of "Lactose" will. Note that the lactose is strained from curdled milk, leaving almost lactose-free curd for cheese production, which is why your hard cheeses have little to no carbohydrates in them, although there is usually enough lactose to trigger a reaction in those allergic to lactose.
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