Saturated Fat and Heart Disease Truth — Transcript

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1. 0:00Is saturated fat a problem for our heart
2. 0:02or not? It's a controversy that people
3. 0:03have been arguing about for decades and
4. 0:05you can easily find voices on both sides
5. 0:07of the question.
6. 0:07>> We're going to talk about why saturated
7. 0:10fats are actually healthy for you.
8. 0:13>> And even if we just look at randomized
9. 0:15controlled trials on this question,
10. 0:17there's at least 14 of those, not three.
11. 0:20And when we put the evidence together,
12. 0:22what we call a meta-analysis, and we do
13. 0:24that rigorously, we see a lower risk of
14. 0:27heart disease events.
15. 0:29>> And the debate got a fresh jolt of
16. 0:30energy recently when the US published
17. 0:32their new dietary guidelines. So though
18. 0:34they keep the old guidance about
19. 0:35limiting saturated fat intake to less
20. 0:37than 10% of calories, there's a shift in
21. 0:40the overall approach to fats. So the
22. 0:41graphic and the text make it clear that
23. 0:43they're moving away from the previous
24. 0:45guidelines recommendations to avoid
25. 0:46full-fat dairy and saturated fat foods
26. 0:49like red meat. So notice the prominent
27. 0:50steak purchased at the top left of this
28. 0:52graphic from the new guidelines. So what
29. 0:54is going on here? Well, I want to
30. 0:56explain how we got here and what often
31. 0:58lies behind the disagreement. And then
32. 1:00I'll give you a picture about what the
33. 1:02data really says. So let's dive in. The
34. 1:04basic question behind the controversy is
35. 1:06this: How does our diet relate to heart
36. 1:08disease risk? Back in the 1950s, there
37. 1:11was a researcher by the name of Ancel
38. 1:12Keys and he felt confident that he knew
39. 1:14the answer and he was getting ready to
40. 1:16gather the data he needed to confirm his
41. 1:18hypothesis in a groundbreaking study. It
42. 1:20was a time when the problem of heart
43. 1:21disease was at the top of everyone's
44. 1:23minds. Now it used to be a minor concern
45. 1:25but it had changed in dramatic fashion.
46. 1:27So in England, two Oxford researchers
47. 1:30carefully examined the official records
48. 1:31and documented a shocking increase in
49. 1:33the numbers of deaths from heart disease
50. 1:35driven by plaque build-up in the
51. 1:37arteries. So of course we're talking
52. 1:39here about heart attacks and strokes and
53. 1:41this condition was killing adults in
54. 1:421945 at a rate 15 times higher compared
55. 1:46to 1921 and the same pattern was playing
56. 1:48out in the US. So deaths from heart
57. 1:50disease went from quite rare in 1900 to
58. 1:53the leading cause of death by
59. 1:55mid-century. And when President
60. 1:56Eisenhower had a heart attack in 1955,
61. 1:59the public attention became laser
62. 2:01focused. What is the cause of heart
63. 2:03disease and if we could do something
64. 2:05about it. There was some early
65. 2:06intriguing evidence that elevated
66. 2:08cholesterol in the blood was a key
67. 2:09driver of plaque build-up in the
68. 2:11arteries and it appeared that not all
69. 2:13cholesterol vehicles were the same. So,
70. 2:15low density lipoproteins, they were most
71. 2:17closely associated with heart disease.
72. 2:20But how does diet connect to that? Well,
73. 2:22Keys proposed that the more saturated
74. 2:23fat in the diet produces higher levels
75. 2:26of LDL cholesterol in the blood. So, it
76. 2:28was a plausible idea and we did have
77. 2:30some experimental evidence at the time
78. 2:32pointing in this direction. But we
79. 2:33needed more data to confirm the link
80. 2:35between diet, cholesterol and heart
81. 2:37disease. So, Ancel Keys had an
82. 2:39innovative approach. He set out to find
83. 2:41groups of people living in different
84. 2:42places who had very different dietary
85. 2:44patterns. In particular, he was
86. 2:46interested in how much fat they ate. So,
87. 2:48his initial research turned up an
88. 2:49intriguing clue. So, cholesterol levels
89. 2:52in the blood, they were closely
90. 2:53associated with the share of total
91. 2:55calories that came from fat. But these
92. 2:57observations came from a relatively
93. 2:58small data set drawing on just a few
94. 3:01places in Europe. So, he set his sights
95. 3:03on a much larger project. He ended up
96. 3:04assembling a massive data set of 16
97. 3:07cohorts of healthy men from selected
98. 3:09populations of across seven countries,
99. 3:11including several in Europe plus the US
100. 3:13and Japan. It was called the Seven
101. 3:16Country Study and the first findings
102. 3:18dropped in 1970. So, Keys' initial ideas
103. 3:21were seemingly confirmed that heart
104. 3:23disease was linked to blood cholesterol
105. 3:25levels. And those in turn were linked to
106. 3:27saturated fat in the diet. But not
107. 3:29everyone at the time agreed with his
108. 3:30findings as we'll see shortly. Numerous
109. 3:32studies continued to examine the data
110. 3:34over the years as cohorts aged and the
111. 3:36relationship held. A 25-year follow-up
112. 3:39saw the same strong link between
113. 3:41saturated fat intake and heart disease.
114. 3:43So, that and other lines of evidence
115. 3:44established what became called the
116. 3:46diet-heart hypothesis and is one of the
117. 3:48most important and influential ideas in
118. 3:51public health today. The basic idea is
119. 3:53this, that saturated fat increases LDL
120. 3:56cholesterol in the blood and that in
121. 3:57turn increases heart disease risk. But
122. 4:00as I mentioned at the beginning of the
123. 4:01video, this theory hasn't been without
124. 4:03its critics and the controversy has been
125. 4:05stoked in recent months with a new
126. 4:06meta-analysis of studies on saturated
127. 4:08fat and heart health outcomes. So it
128. 4:11looked at nine different trials
129. 4:12including about 13,000 total
130. 4:14participants. In the included trials,
131. 4:16researchers wanted to look at how
132. 4:18reducing saturated fat intake might
133. 4:20modify the risk for things like heart
134. 4:21attacks and strokes. Surprisingly, the
135. 4:24meta-analysis found that there was no
136. 4:26statistically significant differences
137. 4:27between those who lowered their
138. 4:29saturated fat intake in their diets and
139. 4:31those who didn't. So things get a bit
140. 4:32confusing because other meta-analyses
141. 4:34say different things. So for example, an
142. 4:36important review that was published by
143. 4:38Cochrane in 2020 did find some benefit
144. 4:41in saturated fat reduction.
145. 4:42Specifically, there was a 17% reduction
146. 4:45in the relative risk for combined
147. 4:47cardiovascular events. So this is a
148. 4:49broad measure that groups together a
149. 4:50number of different heart health
150. 4:52problems. So what is going on here? Who
151. 4:54should we believe? This new
152. 4:55meta-analysis or the previous Cochrane
153. 4:57review in 2020? Well, the issue often
154. 5:00comes down to this, which studies get
155. 5:02included in the analyses. So many of the
156. 5:04studies on saturated fat and heart
157. 5:06disease they're now fairly old. So look
158. 5:08for instance at the list of included
159. 5:10studies in that first meta-analysis that
160. 5:11we looked at. Many of them are from the
161. 5:131960s and the most recent one is from
162. 5:162016 and that one is tiny. So there's
163. 5:19not a lot of new data. Instead, the
164. 5:21differences between the meta-analyses
165. 5:22are usually a result of which of these
166. 5:25older studies they include and which
167. 5:26they decide to leave out. So if we zero
168. 5:29in on the list that we just looked at,
169. 5:30you'll see the Minnesota Coronary
170. 5:32Survey. You can also see it's actually
171. 5:34the largest one that they draw on. So
172. 5:36it's an important piece of the analysis,
173. 5:38yet Cochrane does not include it and I
174. 5:40can hear the critics now. They would
175. 5:42claim that the authors of the Cochrane
176. 5:43analysis just want to include studies
177. 5:45that will give them the results that
178. 5:46they want. But that is not the way that
179. 5:48Cochrane reviews work. So authors of
180. 5:50these analyses, they lay out criteria
181. 5:52for inclusion for the studies, and that
182. 5:54acts like a filter. So it makes sure
183. 5:56that we only include studies of high
184. 5:58quality while excluding others. And
185. 6:00these criteria are not arbitrary.
186. 6:02They're built on common understandings
187. 6:03about what makes for good quality data.
188. 6:06And those rules are the basis for all
189. 6:07Cochrane reviews, not just this one on
190. 6:09saturated fat. So in the case of the
191. 6:11Minnesota coronary survey, for instance,
192. 6:14Cochrane does not include it for a very
193. 6:15sensible reason. They focus on just
194. 6:17studies that lasted at least two years.
195. 6:20And the logic here is this. It takes
196. 6:22time for the effects of dietary
197. 6:23interventions to show up. But the
198. 6:25average time that the participants spent
199. 6:26in the Minnesota coronary survey was
200. 6:28just over one year. But even if it had
201. 6:31lasted more than two years, the study
202. 6:32has other serious problems. So for one,
203. 6:35the bulk of the participants, they were
204. 6:36quite young, with the largest group
205. 6:38being under the age of 30. Now we
206. 6:40wouldn't expect to see any benefits of
207. 6:42lowering LDL cholesterol at this age,
208. 6:44particularly for such a short time
209. 6:46frame. The risk of heart attacks in this
210. 6:48age group is close to zero. So no matter
211. 6:50what they're doing with their diet,
212. 6:51they're probably not going to have a
213. 6:52heart attack. The next problem is that
214. 6:54the lower saturated fat diet had a fatal
215. 6:57flaw. It included margarine. Now
216. 6:59margarines at that time had plenty of
217. 7:01trans fats, which we now know are even
218. 7:03worse for your heart than saturated
219. 7:05fats. So this could cancel out any
220. 7:07potential benefits of that intervention
221. 7:09diet. Plus participants, they came and
222. 7:11went from the hospital, and they were
223. 7:12only on the intervention diet when they
224. 7:14were institutionalized. So this is a
225. 7:16classic case of garbage in, garbage out.
226. 7:19Other meta-analyses that include the
227. 7:21Minnesota study will not show a link
228. 7:23between saturated fat intake and
229. 7:25cardiovascular disease. Cochrane
230. 7:27reviews, on the other hand, which only
231. 7:28include high-quality data, show the link
232. 7:31clearly. And even if we move away from
233. 7:33randomized clinical trials and just
234. 7:34observe the population, what do we find?
235. 7:37Well, one example included more than
236. 7:38120,000 people in two large cohorts, and
237. 7:42it followed them up for about 30 years.
238. 7:44So, replacing saturated fats with
239. 7:46unsaturated fats was associated with a
240. 7:48significantly lower risk of death. And
241. 7:50finally, a key piece of evidence is
242. 7:52this. We've got great evidence that
243. 7:54saturated fat intake raises LDL
244. 7:56cholesterol levels, which is a critical
245. 7:58risk factor for heart disease. There's a
246. 8:00consistent pattern here in the research
247. 8:01despite what you'll see on social media.
248. 8:03So, we can see it for example in this
249. 8:05analysis of 200 studies. Higher amounts
250. 8:08of LDL cholesterol in the blood
251. 8:10correlate with higher rates of heart
252. 8:12disease. And the link is so strong that
253. 8:14those study authors conclude that the
254. 8:16evidence clearly shows that LDL causes
255. 8:19heart disease. And in that analysis,
256. 8:20they looked at observational data,
257. 8:22randomized clinical trials, Mendelian
258. 8:24randomization trials. The data is clear.
259. 8:26But then the next question is what if
260. 8:28you're otherwise healthy? So, you'll
261. 8:29hear online that if you're a perfect
262. 8:31weight or you don't have diabetes, you
263. 8:32don't have issues with insulin
264. 8:33sensitivity, if your blood pressure is
265. 8:35perfect, then you don't need to worry
266. 8:37about blood cholesterol levels. Well, an
267. 8:39important study called the PESA study,
268. 8:41PESA, answers that question. So, we can
269. 8:44see that blockages in our arteries, they
270. 8:46can develop if the LDL cholesterol
271. 8:48levels are above 50 to 60 mg per
272. 8:50deciliter, even if all of the other risk
273. 8:53factors such as insulin resistance are
274. 8:55perfect. So, the link between saturated
275. 8:57fat and heart disease is strongly
276. 8:59supported by several different types of
277. 9:01evidence. But there is some important
278. 9:03nuance here. I do not want to overstate
279. 9:04the significance of saturated fat in the
280. 9:06diet. The impact of reducing it might be
281. 9:08more pronounced in some populations
282. 9:10compared to others. So, a study for
283. 9:12instance that was published at the end
284. 9:13of last year found that for individuals
285. 9:15who are at low risk, if they reduce
286. 9:17their saturated fat intake, it has
287. 9:19little benefit over a five-year period.
288. 9:21But for those at high risk of heart
289. 9:22disease, cutting their intake yielded
290. 9:24significant reductions in the risks of
291. 9:26death and heart disease. Saturated fat
292. 9:29intake is not the only factor that we
293. 9:30should be paying attention to, nor is it
294. 9:32even the most important. We want to
295. 9:34boost fiber intake if we don't have
296. 9:36irritable bowel syndrome or inflammatory
297. 9:38bowel disease, we want to make sure we
298. 9:39get plenty of exercise. We avoid alcohol
299. 9:41and smoking. We want to keep our blood
300. 9:43pressure under control, maintain a
301. 9:44healthy weight, and manage our stress
302. 9:46levels. The greatest benefits, in terms
303. 9:48of heart health, they come from
304. 9:49optimizing all of these areas, rather
305. 9:52than just obsessing over one. Now, at
306. 9:54the outset of this video, I did mention
307. 9:55the new dietary guidelines, and there
308. 9:57have been some worries about them. Now,
309. 9:59before they came out, I was worried that
310. 10:01they'd be full of problems, but as it
311. 10:03turns out, I was pleasantly surprised by
312. 10:05some of the things that they contain.
313. 10:06Now, it is a mixed bag, so make sure to
314. 10:08check out this next video here to see
315. 10:09what they got right and where they go
316. 10:11off course.