Saturday, March 7, 2009

Intermittent Fasting with a Condensed Eating Window – Part II: Blood Pressure, Body Weight & Cholesterol

Is fasting and eating huge meals bad for blood pressure?
Is fasting and eating huge meals bad for blood pressure? (Photo by ooOJasonOoo)

In the last post, we looked at changes in glucose tolerance and insulin sensitivity in people who were put on an intermittent fasting regimen. Continuing with the same study, it's time to look at the effects of a reduced meal frequency on blood pressure, body weight and cholesterol levels.

You can find a more detailed description of the two papers and the methods used in the study in the previous post (Intermittent Fasting with a Condensed Eating Window – Part I: Poorer Insulin Sensitivity and Glucose Tolerance?), so I won't talk about them too much here. Just to summarize briefly: The volunteers were divided into two groups, with one group eating 3 meals spread throughout the day (breakfast, lunch and dinner), and the other one eating only one meal from 4:00 PM to 8:00 PM. The 1-meal-per-day group was told not to reduce their calorie intake, making their diet a condensed eating window version of intermittent fasting without caloric restriction.

Blood pressure

Systolic and diastolic blood pressures were higher in the 1-meal-per-day group (116.1 and 69.8, respectively) than in the 3-meals-per-day group (109.5 and 66.0, respectively). Again, a surprising result, considering that animal studies usually show an opposite effect. Even in studies on overweight humans, fasting seems to result in lower, not higher, blood pressure.

So, perhaps this means that while fasting itself may be beneficial for blood pressure, eating a huge meal after the fast is in fact harmful? Maybe, but as with the blood glucose and insulin results discussed in the previous post, there are a few things to consider before drawing that conclusion.

First, even the subjects on an intermittent fasting diet had their blood pressure levels within the normal range. Yes, there was an increase, but whether this increase was detrimental to health is a whole different issue. Second, and this is a crucial point in my opinion, the measurements were taken at different times: early morning in the 3 meals/d group vs. late afternoon in the 1 meal/d group.

I think a more reasonable comparison would have been achieved if blood pressure was measured early in the morning in both groups (the same thing might not be true of blood glucose and insulin measurements, however; see Part I for details). Many bodily functions seem to slow down at night, and it takes a while for everything to pick up again after you wake up. If you've ever measured your body temperature right after you wake up, you've probably noticed that it can be considerably lower than during the day. Indeed, the intermittent fasting group had slightly higher body temperature than the control group, though this was not statistically significant.

Body weight and fat mass

Finally, we get to take a look at some good news regarding condensed eating window diets. At the end of the experiment, the intermittent fasting group weighed less than the control group (65.9 kg vs. 67.3 kg, respectively). Fat mass was also lower in the fasting subjects (14.2 kg) than in the non-fasting subjects (16.3 kg).

Before you get too excited – as if there has been much to get excited about so far – there's a small caveat: The fasting group ate slightly less. Even though the subjects were told to eat enough to maintain their body weight and the experimenters tried to control for calorie and macronutrient intake, the one big daily meal eaten by the fasting group didn't add up to the three smaller meals. Here's a quote:

The average daily energy intake across treatments was 2364 kcal in the 1 meal/d diet and 2429 kcal in the 3 meals/d diet.

Thus, the intermittent fasting group ate 65 kcal less per day. That's a pretty insignificant reduction, but why couldn't they just have forced that one last piece of chocolate down their throats just to make the numbers match? Still, even if you put the 1.4 kg of weight lost by the fasting group down to eating less, the more impressive 2.1 kg reduction in fat mass probably had more to do with eating less often.

HDL, LDL and triglycerides

Total cholesterol levels were higher in the 1-meal-per day group (216.5 mg/dL) than in the 3-meals-per-day group (191.0 mg/dL). Since total cholesterol levels tell us very little about health, a more detailed look at the levels is in order.

Both HDL and LDL were increased in the fasting group. HDL was 61.9 mg/dL in the fasting subjects and 56.7 mg/dL in the control group. LDL levels were 136.2 mg/dL and 113.3 mg/dL, respectively. Calculating the ratio of HDL to total cholesterol, which is a more useful marker than total cholesterol, we get 0.286 for the intermittent fasting group and 0.297 for the control group. Not a dramatic difference there.

As I've mentioned before, even though most people would call LDL the "bad" cholesterol and HDL the "good" cholesterol, it's not quite that simple. With LDL, the important thing is the size of the particles; the smaller their size, the more harmful they are. Unfortunately, there's no distinction between LDL and VLDL (very low-density lipoprotein) in the paper. Triglycerides, which correlate with VLDL, were lower in the fasting group (93.2 mg/dL) than in the control group (102.2), but this result was just below the threshold of statistical significance (P = 0.08).


Subjects consuming only one meal per day had a slightly higher blood pressure than subjects eating three meals per day. This effect may be due to the fact that blood pressure was measured at different times in the two groups, however.

Body weight and body fat mass were reduced in the 1-meal-per-day group. Despite attempts to control for energy intake, subjects eating only one meal ended up eating 65 kcal less than subjects in the control group, which may have affected the results.

Total cholesterol was higher in subjects eating only one meal. This increase resulted from an increase in both HDL and LDL, with little change seen in HDL/LDL ratios between the groups. Triglycerides tended to be lower in the fasting group, but the result was not statistically significant.

In the third and final part of this series, we'll be looking at the remaining data from the blood sample analysis and wrapping things up.

For more information on intermittent fasting, see these posts:

Intermittent Fasting with a Condensed Eating Window – Part III: Fasting Blood Glucose, Cortisol & Conclusion
Intermittent Fasting with a Condensed Eating Window – Part I: Poorer Insulin Sensitivity and Glucose Tolerance?
Intermittent Fasting Reduces Mitochondrial Damage and Lymphoma Incidence in Aged Mice
Intermittent Fasting Experiment - Update after 5 Months

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2 kommenttia:

Calculating cholesterol December 14, 2009 at 5:35 AM  

I have looked at many sites on this subject and not come across a site such as yours which tells everyone everything that they need to know. I have bookmarked your site. Can anyone else suggest any other related topics that I can look for to find out further information?

Anonymous April 5, 2012 at 6:35 PM  

Do you have the temperature readings of this study?

You mentioned it, but didn't post the results-thanks

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